Will this version of the phone work on AT&T/T-Mobile? - Motorola Droid RAZR

I've been searching high and low for a phone that will work on both T-mobile and AT&T. The Galaxy Nexus was going to be my choice, but it has way too many problems (screen being the biggest issue).
I found this version of the Razr Maxx which says that it has bands for both AT&T and T-Mobile. My question to you guys is this: If I buy this phone, will I be able to use it and get full 3G (HSPA+) speeds on either carrier?
http://www.clove.co.uk/motorola-razr-maxx
Thanks!

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After doing some more research, it seems that the phone has to have 1700/2100 bands in order to work on T-Mobile.
The phone has 2100 band. Does this mean that T-Mobile 3G HSPA will work only when the area has that band, or not at all?

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That model runs on :
GSM/GPRS Yes
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Frequencies850/900/1800/1900 MHz
and/or
3G/HSPA Yes
Frequencies2100/1900/900/850 Mhz
So YES, that model WILL WORK on ATT/TMO. Both companies have roaming agreements with each other and other companies which would allow your device to work if and when you are within a coverage area. NOT ALL features may work in certain areas AND data may be a certain speed in 1 area and in another it may be MUCH MUCH SLOWER due to the fact that it is using your 2G/GSM bands because there is no 3G/HSPA aka HSPA+ aka 4G (aka by ATT and/or TMO). This particular model CANNOT AND WILL NOT ever get true 4G/LTE.
Hope this helps...

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Thanks for the answer. After doing a lot of research, I've learned that it WILL work for AT&T 3G/"4G" speeds, and will NOT work for T-Mobile 3G/"4G" speeds.
Reason being is that even though it has the 2100 band, it doesn't have the 1700 band, which T-Mobile requires for full HSPA speed. It uses one for uplink and the other for downlink. So even though it has one of the bands, I'll never be able to get full speed 3G on it.

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ajm786 said:
Thanks for the answer. After doing a lot of research, I've learned that it WILL work for AT&T 3G/"4G" speeds, and will NOT work for T-Mobile 3G/"4G" speeds.
Reason being is that even though it has the 2100 band, it doesn't have the 1700 band, which T-Mobile requires for full HSPA speed. It uses one for uplink and the other for downlink. So even though it has one of the bands, I'll never be able to get full speed 3G on it.
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after many years of following this stuff, and as a user of both tmo & att services, i must say you are exactly correct! i vaguely recall reading about a pentaband phone in development that would do 3g on both services, but lost track of whether it ever came to market
edit: turns out pentaband phones exist:
forums.androidcentral.com/android-hardware/170487-pentaband-phones.html
i'm surprised the RAZR wasn't developed as penta...