My wife uses an application called VOIPbuster quite a bit to make calls to exotic countries from her cell phone. She claims that her phone# is displayed as CLID at the remote end.
Just an update on this old saga, for anybody who cares 
VOIPdiscount turned out to be near-useless, with completely nonfunctional calls to France or Germany, and most texts send to anywhere (except to myself) not delivered.
Having given up on incoming VOIP (which is just too difficult to configure manually, and even if you have an app which takes care of the various keep-alive requirements will drain your battery fast; well under a day on most smartphones, except for Apple) I have gone back to DIDlogic which works great.
Except… wait for it… bloody Vodafone UK are now blocking VOIP on all contracts below £40/month. This started earlier this year, evidently. There is an option to buy a 2GB/month data add-on for £10/month, which makes the cheapest VOIP option £20/month. So VOIP needs WIFI now. So, why not dump Vodafone? Their Euro Traveller deal, £2-3/day to transfer all free allowances to anywhere in Europe, is not matched by anybody.
Sorry, when I said it uses no extra battery I meant over and above having push notifications turned on, which I (and most people) do already for everything else that uses them.
I wonder how they implemented that…
There is a good explanation here . It does hit battery life (seems to take about a quarter away on my 4G iPhone), but it works very well when you’re in range of a 3G/4G/wifi signal.
The only issue with always-on internet is battery life. Apple have done an excellent job of optimising this particular system so that latency is low without running the radio 100% of the time.
Then when that proxy gets an incoming call it sends a notification to the phone using the always-running APNS (Apple Push Notification Service)
I wonder how they implemented that…
This is an old issue in industrial remote-site data collection and it is always done with either always-on internet, or by making a GSM call to the remote device. Or sending it an SMS request to go online etc…
What is the battery life like?
Battery life is fine (as fine as any smartphone device). It doesn’t need to keep the app running to get incoming calls. When the app isn’t in the foreground it signals to an online proxy that it should register with the SIP server as the client for incoming calls. At that point the app can quit/sleep/whatever. Then when that proxy gets an incoming call it sends a notification to the phone using the always-running APNS (Apple Push Notification Service). You hit the button on the incoming notification and it launches the app which answers the call. It’s more reliable than it sounds! The phone has to be listening for the incoming messages, but all iOS devices are doing that ordinarily anyway; the CPU and display sleep and the radio (wifi or cellular) wakes them as necessary, so battery use is minimal.
Acrobits also support letting the app go to the background and it will wake up and bring itself to the foreground, but to use that you need a SIP VOIP provider that supports using TCP for signalling, which few do. And it’s still less efficient than the notification method.
Using Acrobits on an iPhone it works with any number of VoIP providers, you put in the most basic details (phone number, server address, password), and it just works, incoming and outgoing, with no need to keep the app running, etc. etc.
What is the battery life like? That is one bit I can’t see any way round. The only way to get an incoming call to work is by the phone being online solidly – unless somebody is doing something clever using GSM signalling which, of course, is how mobile phones ring instantly for incoming calls while the phone talks to the tower only about once every 10 mins which is today’s practice.
Peter, for someone involved in a technology business you seen ever so conservative with your use of technological products, what with your Symbian phone, your MFD, and your aversion to Garmin and Aspen
Too damn right, and I don’t buy shares in IT companies either 
Actually I am at the leading edge with the phone – just flashed it with custom firmware. That’s a really funny story… how all that Nokia stuff escaped into the wild I now have really useful little things like a permanent retry on SMS so you can send an SMS even at FL150 … eventually. Old phones used to do that but it was banned some years ago. Plus I can browse my PC with the phone, over wifi.
The funny thing about IFR is that no two pilots work the same way. Developing a “private IFR” course would be quite a challenge, and I would never want to do even a talk on anything to do with IFR flying to existing IFR pilots.
Peter, for someone involved in a technology business you seen ever so conservative with your use of technological products, what with your Symbian phone, your MFD, and your aversion to Garmin and Aspen
Peter, I do think part of the reason that you have problems with this stuff is because of using the less ubiquitous options. Using Acrobits on an iPhone it works with any number of VoIP providers, you put in the most basic details (phone number, server address, password), and it just works, incoming and outgoing, with no need to keep the app running, etc. etc. Ditto the Skype client on iOS or Android, which if all you want to do is phone the US cheaply once in a while is perfect. I know you like your phone for its camera but “One could waste one’s life on this stuff” means that choosing spec versus popularity is always worth considering.
