Guys, one thing to note is that CM7 (and in turn MIUI), don't like multiple APNs. AT&T runs their ROMs with two different APNs, keeping the data APN separate. This is fine on any ROM based on AT&T's releases, however, if you try to use two on CM7, you'll likely run into issues. The best thing to do is disable the "phone" APN and only use the "wap.cingular" APN. If you have both on your phone, you can do this by adding "default" to the list of APN types for the "wap.cingular" APN (or you should be able to entirely delete, just make sure to add default to "wap.cingular").
If you do run an AT&T based ROM, I highly suggest you do use both with "wap.cingular" for mms and supl APN types, and "phone" for default. This is the absolute only "trick" you can do to make the phone's data a little faster (since build.prop changes don't do anything).
Here are the details for both:
"wap.cingular" APN:
Name: ATT MMS
APN: wap.cingular
Proxy: Not set
Port: Not set
Username: Not set
Password: Not set
Server: Not set
MMSC:
http://mmsc.cingular.com
MMS Proxy: 66.209.11.32
MMS Port: 80
MCC: 310
MNC: 410
Authentication type: Not set
APN type: mms,supl (and default if you are only using this APN)
APN protocol: IPv4
"phone" APN:
Name: ATT
APN: phone
Proxy: Not set
Port: Not set
Username: Not set
Password: Not set
Server: Not set
MMSC: Not set
MMS Proxy: Not set
MMS Port: Not set
MCC: 310
MNC: 410
Authentication type: Not set
APN type: default
APN protocol: IPv4
I notice a definite increase in response time with the "phone" APN. Pages seem to load a lot faster, regardless of what actual speed increases it gives you, so I recommend using that if you aren't on CM7 or MIUI. If you are, well, stick to single APN or else you'll see data issues, especially in Market.
It's not "internet + mms", you specifically type in "internet,mms". It is just a text field. You have to type in what you want. Actually, "internet + mms" may be a valid setting in that field, but I've always seen it comma separated, so that's what I'd stick to. I'm not sure what valid APN types there are, the ones I know of are mms, supl, internet, and default. default obviously being the catch all for anything not configured in another APN.