Wednesday, 12 June 2013

Replacing A&A mobile service

The loss of A&A mobile phones was a bit of a wrench. I have been used to having a mobile that works with the phone system properly, busy lamp fields, call pickup, and so on.

So, I have been looking for a replacement. It is possible to use a data SIM in the iPhone, but with our data SIMs the texting does not work, so only iMessage. We use texting a lot for nagios, so I had to get some simple contract and there are some that allow lots (unlimited even!) data.

So, can you use SIP on an iPhone over 3G?

So far the answer is yes! There are a lot of SIP clients that seem tied to specific SIP providers. But this one "3CX" was the first when I searched for SIP and rather shockingly seems to just work.

I have turned off STUN, NAT helper, and echo cancellation, forced a-law audio (probably unnecessary), and registered to my FireBrick. The NAT helper and STUN has to be off so that the FireBrick sees it is NAT and does the needful, but then it does work.

The result is a phone that, well, works. The audio quality is perfect (only tested from my house where I have good coverage). Ironically there was some initial break up when using WiFi but on 3G it was faultless. The NAT keep alives work. The app switches WiFi and 3G cleanly, re-registering. Not tried taking a call on WiFi out of range, that would be a challenge I expect, though I may be able to do some sort of call park I expect. I can hold and call transfer cleanly. It means I can record calls (though the app offers that as well!).

I can arrange for incoming texts to relay to the phones "real" number, leaving me only with outgoing texts not using my normal number. Apparently if I had an android then there is an app for that too :-)

Of course, the nice thing is, I can set incoming calls to try SIP and fall back to calling the mobile number. That way I get the best of both worlds.

I'll see how it goes, but so far I am impressed.

Update: Some maths. If we used a data SIM which we charge 2p/MB+VAT for, an a-law call is 160 bytes a-law plus 12 bytes RTP plus 8 bytes UDP plus 20 bytes IP, so 200 bytes each way per 20ms, so 20KB/sec usage. That works out 1.2MB/min which is 2.4p/min for the mobile leg. That is not far off what we did before. Shame data SIMs can't handle text else this would be a very close solution.


  1. We use it a lot for testing and with its best mate the VoIP PBX too and I really like it. That said, so far I've been unable to beat the Android one on the Galaxy for quality and handover - while its not perfect, it will hand over between 3G and wifi - critical in my house as Orange don't deem us (or the rest of the street) worthy of coverage other than GPRS unless sitting on the roof. Definately worth a look too..

  2. I tend to use Counterpath Bria on Linux, Windows, iOS and Android. It's commercial (mobile versions about £9 per platform, desktop $50), but worth it I think.

  3. No experience of the iPhone, but I've been using SIPDroid to connect my Android phones to my Asterisk server for about 4 years and it works well over both wifi and 3G. I have it set to use the 11Kbps Speex codec over 3G and G.722 over wifi.

    One minor annoyance with wifi is that wifi roaming seems very badly supported by most wireless chipsets - my phone won't let go of an access point until its signal is extremely weak, so wandering around is a problem.

    My cheapy PAYG Three SIM has a out-of-bundle price of 11p/MB; Speex is VBR up to 11Kbps in each direction, so assuming a worst case of sending and receiving at the maximum data rate the whole time, that works out at 165 kilobytes per minute (excluding protocol overheads), which I make out at 1.77p/minute.. beats the 26p/minute that Three charge PAYG customers for PSTN calls, even after protocol overheads are taken into account. :)

    Of course, I never allow my data bundle to run out, so it works out orders of magnitude cheaper than that in reality. The data bundles go for £5 for 2 gig, so that works out at 0.035p/minute, and you get 150MB "free" on every top-up, which equates to about 15 hours of VoIP.

  4. Yep, 'just works' fine here on iPhone on 3G, but not on the (Guest) WiFi I have access to during the day which presumably has multiple ports closed.

  5. I've had poor performance on my Android phone - admittedly, not on AASIP, and connected to Vodafone. Losing the connection all the time, crap call quality - though some interesting results at times.