It should work fine as long as you purchase the phone outright. They won't give you the phone for the $260 price without a contract (as you probably know). The question that I have though is will the $50 plan give you all of the data that you'll want for a phone of that caliber? Do you really need that phone for an account like that? You might be much happier (and slightly richer) if you just got something less expensive like a MyTouch 4G. To me, it's sort of like buying a Ferrari to drive back and forth to Safeway.
However, if you choose to go with that phone, it should work fine with the monthly or prepaid plans.
Because the Amaze as well as the Galaxy SII are designed to make heavy use of the data service, most likely the 50.00 plan will not give you enough data transfer. The Value plan for 54.99 only gives you 200 MB of transfer, after that 0.10 per MB overage. The prepaid plan for 50.00 will slow the speed after the first 100 MB. Either way, you have to pay the retail price for the phone, and you will not be happy with the data usage. If you want a good phone, you need a good plan.
Both of those plans are great plans, but not for this caliber of phones.
If you want to get a really awsome phone with a cheap plan i think thats a great idea! even thought it is expensive look at the positivess:
1.you get a cheap plan
2. all phones a wifi capable so if you have wifi or acess at least your good
3.NO CONTRACT. dont be locked into a contract for a cool phone even though its like what 600 bucks your saving like 1000 bucks on a contract a year.
4. unless you talk on the phone non stop for 30 days straight you should get a plan with fewer minutes (cheaper)
5.your phone is an investment and its like a mini comp. keep in mind this phone will problably bring lots of useful things to you and it will become a very important part of your life so dont think a phone that expensive isnt worth it on a prepaid plan.
6. it is unlimited data just not as fast. you are problably around wifi alot of the time and dont even know it. try to take advantage.
7. IT MAKES SENSE.personally a prepaid plan is a great option to go with. if you have the money to buy a phone get it. prepaid has essential feature of a contract plan and in some cases they are the same except without the phone discount.
lastly, if you want a phone (even if its super expensive) make sure its great. if you get a lame phone you get bored of it fast and you dont get the cool features about a phone. it loses its attactiveness. usually the more expensive phone have the better features..