The State of SIP

How well does SIP work on a modern Android phone, with no 3rd party apps?

I'm trying to give up my mobile phone contract. As part of that, I'm switching my voice calls to VoIP providers. For family and friends, that usually means WhatsApp, Skype, Signal and other consumer apps. For work, Hangouts, Zoom, and Skype.

But what about "normal" people who just want to dial a PSTN number?

And what about "abnormal" people who want to dial my VoIP directly?

These are my experiments using the OnePlus 5T running Android 10, using the native Android dialler.

Inbound PSTN to SIP - working!

In my previous blog post - Adding SIP calls to Android for free! - I described how to get set up with a free SipGate Basic account.

Now, if people ring a landline phone number, it redirects to my SIP. Which means my Android phone just starts ringing and I can answer like normal. It works even if I only have WiFi coverage. Magic!

Outbound SIP to PSTN - working!

Just works! Using SipGate I can call out from my phone - assuming I've told Android to let me pick which SIM to call from.

Or, I can go to the SipGate website and type in a phone number. My SIP line calls me and, once I'm connected, calls out to the other number.

As a bonus, their per-minute call rates are much cheaper than my mobile provider!

Sadly, SipGate don't support SIP-to-SIP calls. So I've set up another SIP account on my phone.

Inbound SIP to SIP - working!

Most SIP provider websites are terrible. The least-worst one that I found which was offering free pure-SIP accounts was IPTEL.org.

People with SIP phones can call me directly on edent@iptel.org. Woo!

Outbound SIP to SIP - broken 😞

When I try to call a SIP number using my IPTEL account, nothing happens.

Android asks which "SIM" I want to call from. I get a dialler screen, but it never connects. There's no ringing. No error tone. Nothing.

I'm on my home WiFi with no port filtering. I don't have a VPN running. I'm trying to call music@iptel.org - a SIP account which just plays music. I can call it from my desktop and mobile browser using the free jssip.net website.

But if I try the same thing using my phone SIP dialler - it never connects. I've tried calling a friend's SIP number - and it never connects. I've tried with and without and outbound proxy. Still nothing.

I can obviously make SIP calls via SipGate - but that only goes to the PSTN.

I can receive SIP calls - whether originating from the PSTN or other SIP users.

Perhaps IPTEL don't support it? I tried LinPhone - but that couldn't make SIP calls either, unless I downloaded their Android app. Even that was a bit iffy.

In my whole circle of telco geeks, I only found three people with SIP accounts. I could only make calls to one of those. The others failed to connect - but there was no useful info in their logs. Huge thanks to Ben and Matt for helping me test.

I'm done

At which point, I'm beaten. I'm going to give up trying to make SIP to SIP calls. As it happens, I only know one person who regularly uses their own SIP account. Hi Neil!