Is AT&T blocking SIP

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.