Please confirm what I learned about buying an Android phone for ST

[__0]

I think I got it right, but don't want to make a costly mistake if I missed something.
As I understand it, I need to buy a non-subsidized phone listed on AT&T site. Other ones will probably lack the AT&T 3G frequency. The phone will work even if still SIM-locked to AT&T.
T-Mobile compatible phones are to be avoided.
Is everything above correct?
Also, are there any alternatives to AT&T stores in purchasing the phone?
If I buy a 4G phone, will it achieve 4G speeds?

[MrBooMY]

Get a phone off of craig's list like I did. I love my captivate on ST.

[october262]

I think I got it right, but don't want to make a costly mistake if I missed something.
As I understand it, I need to buy a non-subsidized phone listed on AT&T site. Other ones will probably lack the AT&T 3G frequency. The phone will work even if still SIM-locked to AT&T.
T-Mobile compatible phones are to be avoided.
Is everything above correct?
Also, are there any alternatives to AT&T stores in purchasing the phone?
If I buy a 4G phone, will it achieve 4G speeds?

one thing you left out is you are gonna need an activated sim from the nokia e-71 or nokia 6790.
you can use a tmobile phone but you will not get the 3G speeds only edge