Choose registration or source-IP authorization first
Zadarma documents a login-and-password connection that registers to sip.zadarma.com and a separate trunk model authorized by confirmed static source IP addresses. Creating the IP-authorized trunk consumes an existing SIP login as its identifier and makes that login unavailable for registration. Record the selected model, account owner, credential or approved addresses, signaling target and caller-ID policy before configuring the PBX.
Do not leave both procedures partially active or treat an IP-verification call as registration. A confirmed address, successful REGISTER and completed outbound call are different states. Retain a redacted request and response for the exact path in use.
Documented service facts
Reviewed 2026-09-28. Compare SIP trunk services →
Authentication
DocumentedZadarma documents two connection models: a SIP login and password, or a trunk authorized by confirmed static source IP addresses. The IP-authorized model consumes an existing SIP login as its identifier and makes that login unavailable for registration. Record the selected model, source addresses or credential owner and the permitted caller-ID numbers; do not combine the two procedures.
SIP registration
DocumentedThe login-and-password path uses registration to sip.zadarma.com. The IP-authorized trunk explicitly disables registration for the selected SIP login and accepts outbound traffic only from confirmed addresses. Preserve registration, source-IP verification and call completion as separate evidence states.
Inbound delivery
DocumentedZadarma documents routing a virtual number either to a registered SIP login or, for a customer server, to an external SIP URI without registration. The IP-authorized outbound trunk does not itself receive calls on its identifying login. Keep number ownership, inbound target, allowed provider source addresses and delivered called-party identity distinct from outbound authorization.
Inbound failover
Not verifiedZadarma permits several confirmed source IP addresses for outbound authorization, including main and reserve customer links, but that does not document inbound destination order, failure detection, retry rules or established-call survival. The reviewed public pages do not establish a customer-controlled inbound failover policy. Obtain the exact number-route behavior and test every approved fault and restoration path.
Number and regional availability
Not verifiedZadarma markets virtual numbers in 110 countries and number porting in 40 countries. Exact inventory, portability, identity documents, activation time, caller-ID rights and inbound features remain specific to country, number type, account and date. Verify the selected number in the ordering flow and retain the applicable requirements.
Audio codecs
DocumentedZadarma's current FreePBX PJSIP guide instructs users to leave A-law and mu-law enabled, and its Asterisk IP-trunk example likewise permits alaw and ulaw. A configuration example is not proof of negotiation on every destination. Preserve the offer, answer, payloads, DTMF result and any transcoding for each required route.
T.38 fax
Not verifiedThe reviewed trunk and PBX setup pages do not establish T.38 support or route-specific fax behavior. Zadarma separately documents receiving fax in its hosted PBX, which is not evidence that a customer SIP trunk negotiates T.38 or carries in-band fax reliably. Confirm the exact route and qualify approved documents end to end.
Signaling and media encryption
DocumentedZadarma publishes TLS signaling on port 5061 with SRTP for third-party clients and provides a FreePBX example using TLS 1.2 and SRTP via SDP. The example disables server-certificate verification, so it must not be copied as proof of authenticated transport. Establish certificate validation, SRTP profile and downgrade policy for the deployed PBX and inspect the negotiated leg.
Concurrent calls and call starts
Not verifiedZadarma says outbound channel limits depend on the selected plan and publishes current examples for Standard, Office and Corporation plans. Those public figures can change by region and package, and the reviewed pages do not establish inbound concurrency, calls per second or burst controls. Capture the account's active limits before any authorized load test.
Emergency calling
Not verifiedNo trunk-specific emergency-calling activation, validated location, callback, number eligibility or approved test procedure was verified in the reviewed public setup and number pages. Country coverage and a local number do not establish emergency access. Obtain written route and location requirements for every operating site and retain an independent fallback until accepted.
Pricing model
DocumentedZadarma publishes pay-as-you-go and bundled plans, with outgoing rates, included minutes, numbers and channel allowances varying by region and billing term. A displayed plan is not an account quote. Preserve the dated plan, destination rates, billing increment, included-use conditions, number fees, taxes, currency and renewal term.
Administration and support
DocumentedZadarma documents self-service trunk and number routing, an API and webhooks, and 24/7 chat, ticket and phone support. Its product page also states a 99.9% SLA, but that marketing statement does not define the account's exclusions, credits or response targets. Retain the governing terms, applied configuration, traces and provider case together.
SMS
Not verifiedZadarma offers SMS separately, with inbound availability limited to eligible mobile numbers and country-specific conditions. A voice number or SIP trunk does not establish SMS capability, sender approval, consent, API behavior, throughput or fees. Verify the exact number and messaging program independently.
Build inbound delivery independently from the outbound trunk
The IP-authorized trunk documentation says its identifying login no longer receives incoming calls. Zadarma instead documents routing a virtual number to a free registered SIP login or forwarding it without registration to an external SIP URI. Preserve the number, country requirements, inbound target, provider source addresses, PBX context and delivered called-party identity.
Several confirmed customer addresses can authorize outbound traffic, including addresses associated with main and reserve links, but the reviewed pages do not define an inbound destination order, timeout or retry policy. Do not convert multiple outbound source addresses into an inbound failover claim. Obtain the exact number-route behavior and test failure and restoration separately.
Qualify codecs and protected transport on the deployed leg
Zadarma's current FreePBX and Asterisk examples enable A-law and mu-law. The service also publishes TLS signaling on port 5061 and requires SRTP for third-party clients using that protected transport. Treat those instructions as configuration scope, not proof of negotiation on every destination. Capture the offer, answer, RTP payloads, DTMF result and any transcoding for each required route.
The FreePBX example disables server-certificate verification. Do not inherit that setting without an explicit security decision. Establish the expected server name and trust chain, verify the negotiated TLS and SRTP profiles, and define downgrade behavior. Protection between the PBX and Zadarma edge is not evidence of encryption through the public telephone network.
Keep fax, resilience and capacity unresolved until accepted
The reviewed trunk pages do not establish T.38 or route-specific fax behavior. A separate hosted-PBX fax feature does not prove that a customer trunk negotiates T.38 or reliably transports in-band fax. Qualify the exact number, direction, gateway and approved document set rather than extending a hosted feature to the trunk.
Zadarma publishes plan-dependent outbound channel examples, while inbound concurrency, calls per second and burst controls were not established in the reviewed pages. Provider data-centre and uptime statements likewise do not prove customer-route recovery or established-call survival. Capture the account's active limits and governing SLA terms before bounded resilience or load tests.
Snapshot number, price and messaging conditions
Zadarma markets numbers across 110 countries and porting in 40, but inventory, documents, caller-ID rights, activation and inbound features remain country-, number- and date-specific. Its published pay-as-you-go and bundled plans vary by region and term. Preserve the ordering requirements, dated plan, destination rates, billing increment, included-use conditions, number fees, taxes, currency and renewal terms.
SMS is a separate service whose inbound availability is limited to eligible number types and countries. A voice-capable number or trunk does not establish sender approval, consent, API behavior, throughput or fees. Verify messaging independently and do not represent public pricing as an account quote.
Resolve emergency service and prove the complete call set
No trunk-specific emergency-calling activation, validated location, callback behavior or approved test procedure was verified in the reviewed public setup and number pages. A local number or country listing does not establish emergency access. Obtain written requirements for every service location and retain an independent fallback until the PBX, number and carrier route are accepted.
Pilot registration or source authorization, inbound and outbound identities, codec and DTMF behavior, TLS and SRTP, number routing, failure and restoration, support escalation and every required country route separately. No Zadarma account, trunk, registration, number, call, codec, fax, encryption, failover, capacity, emergency call, message, price, availability or support response was tested for this guide.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.
- Zadarma SIP trunk service ↗
- Zadarma IP-authorized SIP trunk FAQ ↗
- Zadarma server delivery by SIP URI ↗
- Zadarma Asterisk IP-authorized trunk setup ↗
- Zadarma FreePBX PJSIP setup ↗
- Zadarma TLS and SRTP connection guidance ↗
- Zadarma hosted-PBX fax FAQ ↗
- Zadarma price-plan comparison ↗
- Zadarma United States number catalogue ↗
- Zadarma SMS service ↗
- Zadarma SMS rates ↗
- Zadarma API documentation ↗
Examples require adaptation to your topology. No live PBX or hardware testing is claimed.