How to Set Up a SIP Softphone on iPhone and iPad with SIPdia

To set up SIPdia on an iPhone or iPad, sign in, enter Server, Transport, Username and Password on the Account tab, and tap Add and Register. Allow the microphone, local network and notification prompts when iOS shows them. Once the account is registered, calls ring on the system call screen like a regular phone call. One thing to understand from the start: the app must be open to receive calls. SIPdia does not use push notifications, and it unregisters about 20 seconds after you leave it. This tutorial covers the setup, the call screen, audio routes, recordings, and how to work around that limit with forwarding.

SIPdia runs on iOS and iPadOS 17 or later. It uses the same call engine and settings as the Mac app, so if you already have a working account on a Mac, the same details work on the iPhone.

What you need

From your PBX administrator or your SIP provider's portal:

• The server address, with :port only if the server uses a non-standard port.
• The transport: UDP, TCP or TLS.
• The username. On a PBX this is the extension number.
• The password.
• Optionally an auth username, a separate domain or an outbound proxy, if listed separately.

Step-by-step setup

1. Sign in. SIPdia opens on a sign-in screen. Sign in with Apple or Google. SIP accounts register only after you sign in.
2. Open the Account tab. The app starts on the Account tab after sign-in.
3. Enter the server. In Server, type the host name or IP address. Add :port if needed, for example sip.example.net:5080. Without a port, SIPdia does a DNS SRV lookup and then uses the default port for the transport.
4. Choose the transport. Set Transport to UDP, TCP or TLS, as your PBX or provider documents.
5. Enter the credentials. Type the Username (the extension number on a PBX) and the Password. Optionally set a Display name.
6. Advanced fields. Fill Domain, Outbound proxy or Auth username only if the provider lists them separately. STUN server, ICE and Encrypt audio are explained below.
7. Tap Add and Register. SIPdia sends a REGISTER request to the server. The dot next to the account turns green when the server accepts it.
8. Allow the permissions. iOS asks for the microphone, the local network and notifications. Allow all three. The local network permission is required to reach a PBX on your Wi-Fi; Apple's TN3179 explains the prompt. Notifications are used for missed-call alerts.
9. Add another account if you have one. Tap Add at the top of the Account tab and repeat. On the free plan only the default account registers; the others stay saved and show Needs Premium. SIPdia Premium removes the limit.

Making and receiving calls

• Make a call. Type a number on the Phone tab and tap the green button. Tapping it with no number brings back the last number called. With more than one account, pick the account to call from with the From picker on the dialpad.
• Receive a call. Keep the app open. The call rings on the system call screen, also on the lock screen, thanks to Apple's CallKit. The call shows in the status bar and Control Center, and headset, Bluetooth and car buttons answer and hang up.
• Phone app Recents. SIPdia calls can appear in the Phone app's Recents, and calling back from there opens SIPdia and dials. You can turn this off in Settings.

The in-call screen

During a call you have Mute, Keypad, Speaker, Audio, Hold, Add call, Transfer and Record. The arrow at the top returns you to the app; the green bar brings the call screen back.

• Audio routes. The Audio button switches between the earpiece, the speaker, wired headsets, AirPods and other Bluetooth devices, and CarPlay. Speaker toggles the loudspeaker directly.
• Keypad. Sends DTMF as RTP events (RFC 2833), the method most PBXs and providers expect.
• Add call and Transfer. Add call lets you hold one call and place another. Transfer offers a blind transfer to a number or an attended transfer between two open calls.

Recording a call (Premium)

Tap Record, then tap it again to stop. Each call can be recorded once. A notice before recording reminds you that the other party is not told. The WAV file is saved in the app's Documents folder, which the Files app shows under On My iPhone > SIPdia > Call Recordings. Play and share recordings from the Recordings tab. Share them to save them elsewhere, because deleting the app deletes them.

Behind a router or on mobile data: STUN and ICE

When the server is on the internet and the iPhone is behind a router or a carrier NAT, the most common symptom is one-way or no audio. Under Advanced, set STUN server to a public STUN server such as stun.l.google.com:19302 and turn on ICE. STUN (RFC 5389) discovers the public address; ICE (RFC 8445) tests several paths and uses the one that works. On a PBX you manage, also set NAT handling for the extension (nat=yes or force_rport,comedia). You usually do not need either when connected through a VPN. See One-way audio on VoIP calls for the full checklist.

Encryption

If your server supports TLS, set Transport to TLS and Encrypt audio to Required so both signalling and media are encrypted. The certificate must be valid for the server's name and signed by a certificate authority in Mozilla's root list, which SIPdia bundles. Self-signed certificates and roots added with configuration profiles are not accepted. Without a public certificate, use UDP or TCP over a VPN.

The limit to plan around: the app must be open

What this means in practice:

• After you leave SIPdia, it stays reachable for about 20 seconds. Then it unregisters its accounts so the server sends calls to voicemail or forwarding instead of to a phone that cannot answer. Opening the app registers again.
• A call that is already ringing or connected keeps the app running in the background and on the lock screen.
• Set Forward when not answered (Premium, under Forwarding on the Account tab) to a mobile number or to voicemail. The forwarding is set on the PBX through a feature code, so it keeps working when the app is closed. This needs a PBX with feature codes such as Issabel or FreePBX; providers usually offer forwarding in their portal instead.

If registration fails

• "Could not reach the server". Check the address, port and transport. For a PBX on the office network, turn on Settings > Privacy & Security > Local Network > SIPdia. TLS uses port 5061 unless the Server field names another one, and some networks block it.
• Detailed logs. Turn on Settings > Save detailed logs, close the app in the app switcher, open it again and repeat the problem. Then tap Share Logs. The logs include SIP messages, so turn logging off afterwards.

See SIP registration keeps failing for more causes.

Next steps

• The SIPdia for iPhone page describes the features of the iOS app.
• Learn how call recording works and what Premium adds.
• Setting up a provider account rather than a PBX extension? Follow How to Connect a Softphone to an ISP or Provider SIP Account.