Last night I installed a SIP client (CSipSimple) on my phone, and it worked perfectly on my wireless network. So I said to myself, what about 3G. I gave it a few test and while I get the inbound and can make outbound calls. There is lack of voice data being sent. This was a major let down. So I went to my SIP server and made changes in hopes to get this working, without any change in behavior.
This morning I attempted this once more, with the same not so desirable results. So then I said “let’s try this via VPN. I then setup a PPTP VPN connection from my phone only using the 3G (H+) network, I then setup the a new SIP Connection pointing to my internal IP of my SIP server and like magic I was registered and able to accept inbound calls and make outbound calls.
So now I convinced that AT&T is blocking part of my SIP Call. Well wait, perhaps I should try something else. And that is what I did. I connected to a remote network, and setup a SIP client on a computer to connect to my SIP server via the internet. I was able to register and accept / and place calls with full voice also. I now conclude that AT&T is blocking parts of SIP.
After some Google searching, it seems that AT&T allows SIP on data network, but its only seems to be for those with iPhone plans. Well isn’t that nice.
So there it is, I will use my SIP connection to make calls via VPN, it introduces an extra step but it works. Most of all its secure, so I guess it’s for the best.