First off AT&T sweeps regularly. I had SwirlyMMS working on my 3G phone for over a month without any issues, then yesterday I noticed that I was getting an error when trying to retrieve new pics sent via MMS. The error said " httpd error unexpected response " , so then I tried sending and got another error " forbidden ...blah blah "
The problem was the AT&T swept my account and I was basically blocked. Already knowing the drill I called in and asked that my OTA's be resent and the VLR's be cleared (it's important to have them CLEAR the registry , NOT refresh it). Then like a charm everything worked again.
As posted before these instructions are 100% dead on.... if you follow these steps, ALL OF THEM you shouldn't have any issues with AT&T.
"First off, call 888.892.9760. Make sure you have the rep enable WAP push (There are 2 places in Snooper for them to make the change.) Next, have the rep change your iphone texting plan to a normal non-iphone text plan. (costs the same). Lastly, have them resend your OTA's (over-the-air activation) and CLEAR your vlr's (clears the registry). Power cycle your phone and you should be good to go."
** It's important to note that when I called I verified my account setup then asked for the OTA's to be resent , which the customer service agent did without question.... BUT when I asked for the VLR's to be cleared she immediately asked me to hold, then came back and said she would need to transfer me to Tech Support to troubleshooting. I casually mentioned that I knew she has the ability to do what I asked and inquired why she needed to transfer me. She told me that she was told by a supervisor to do this if anyone with iphones called in asking for this. So basically the front line customer support people have been filled in on why people are calling asking for this.
I went ahead and talked to Technical Support and the lady I spoke with was very nice and did what I asked. She did ask why, and I told her that I was resolving a Exchange Server issue and this was the fix we've used in the past. She slammed out the Clearing of the VLR's , I rebooted the phone and everything works again... until the next time they sweep my account

Here's how my call went:
ATT Customer Support: Hi can I verify all your information.. blah blah blah..
ME: Verified my information
ATT Customer Support: What can I help you with ?
ME: Can you please verify that I'm on a Family Unlimited Texting plan , and NOT an iphone texting plan.
ATT Customer Support: Yes, this is correct
ME: Can you please check both places in Snooper and ensure that WAP is ENABLED in both places
ATT Customer Support: Yes, both setting are correct in our system and it's enabled
ME: Can you please check to see that MMS isn't specifically disabled
ATT Customer Support: No, it is not disabled, however you can not receive MMS on an iphone
ME: Yes I know this but it does make a different for my specific issue
ATT Customer Support: No, it's not disabled
ME: Can you please RESEND the OTA's for this phone number
ATT Customer Support: Yes, just sent
ME: Can you please CLEAR the VLR's
ATT Customer Support: Please hold for a moment
ATT Customer Support: Sir, I have to transfer you to technical support for that, that's what I've been told by my supervisor
ME: Why do you need to transfer me ? I know it can be done from your terminal.
ATT Customer Support: I was instructed by my supervisor to transfer VLR clearing requests to technical support
ME: Please transfer me then
TECHNICAL SUPPORT: Can I verify your account info ... blah blah blah
TECHNICAL SUPPORT: How can I help you today?
ME: I have a pretty straight forward request, can you please CLEAR the VLR's on this phone number.
TECHNICAL SUPPORT: Sure, no problem, what issue are you having ?
ME: I'm having an issue with an Exchange Server, and this is the sure fix for it we've used in the past
TECHNICAL SUPPORT: Ok, one moment....... ok , done, please power off your phone and power it back on
ME: Ok I've done that.... (tested MMS in really quick, everything worked again ) ... thank you it's all better now.
blah blah blah ... small talk.... then thanks to her and off the phone....
** The only other thing I would suggest is maybe not asking about the MMS settings as it shouldn't really matter, but if they've specifically disabled it you'll need that fixed. In my case I already knew it was enabled , but just wanted to verify so I didn't have to call back.
Here are my settings:
MMSC:
http://mmsc.cingular.com Proxy: wireless.cingular.com:80
APN: (blank)
Username: (blank)
Password: (blank)
Image size=medium
useragent=Nokia_N95
** The only reason I have the user agent set to something other than iphone is because setting up a sweep to detect and ban accounts based on user agents is pretty easy, so I figured why tell them I'm an iphone since this setting doesn't matter anyway.
Good Luck !