It appears that the HTC Surround for AT&T has been discontinued. If you go on AT&T and filter all of the Windows Phones, then you will only find the HTC HD7S, the LG Quantum, and the Samsung Focus.
If you put even more effort in looking for the phone, then it will come up with a message. The message will state that:
The HTC Surround (TM) – Gray you’re searching for is no longer available.
We believe that HTC have completely stopped manufacturing the phone as it appears that the Canadian carrier Telus have also stopped selling the phone. We believe that they have stopped selling / manufacturing the phone as it probably wasn’t as popular as the other Windows Phones that were on AT&T.
Microsoft have also brought out several new Windows Phones and so AT&T probably needed to make room for those Windows Phones. So either way this isn’t a bad choice as there are a lot of new and better Windows Phones on AT&T.