ATT phone on T-Mobile network

[Challenged_101]

I just got a killer deal on a ATT S3 phone that I want to use on T-Mobile. While searching how to unlock it, I came across a few posts that suggests that just because a phone can be used on another network doesn't mean all of it's speed and features can be utilized.
I can't figure out if my service here in Portland OR is 1700 or 1900 mhz. I don't want a phone that I can only utilize half it's options. Should I keep it or get a T-Mobile S3?

 

[dontpanicbobby]

t-mobile uses 1700 for 4G LTE data. The AT&T samsung Galaxy S3 use 700 for 4G LTE. The thing is the first t-mobile S3 doesnt get LTE at all it uses HSPA+ for 4G data. You can use HSPA+ on the AT&T S3. This speed test on youtube may help you decide.