Do Google Talk Calls work over 3G on AT&T?

I dunno if this is just my fault or something more sinister.

While the discussion over the AT&T-Facetime controversy was going on, I noticed that for what ever reason my phone wouldn't let me make Google Talk calls over 3G. I always got an error message indicating that I needed to be connected to WIFI in order to initiate or receive Gtalk calls.

However, my friends on Verizon were able to easily make phone calls using Google Talk over their cellular network.

Of course, I don't know if this is AT&T, Google, or if something is just wrong with my phone. You see, I have a Samsung Captivate, but it has a Custom ICS Rom (SimplyAOKP for those interested).

IMO, there are 1 of 3 possible things going on:

1. As the possible case with Facetime over Cellular. AT&T is blocking gTalk from making cellular calls. However, as mentioned before, this phone has a custom rom installed. Technically speaking, AT&T should have no idea what I do with my phone. It's not like the ROM builder put this restriction in??

2. Maybe its just my phone. Maybe the Gtalk app is corrupted somehow? Maybe the ROM Builder put this in? Maybe there is some setting I don't know about? My phone doesn't have a front facing camera and that has something to do with it????

3. It's Google making the restriction. This is the one I fear the most and think is the most likely. My guess is that Google put code in gTalk that says if the network is AT&T, customers can't use gTalk over cellular.

If anyone has insight into this, fill me in.

UPDATE: Here's a screenshot: