i got the galaxy s 2 and just had it working on the SO plan and have data browsing up and running, and yes you need to root it for anything else, i will try those later tho
i would imagine that the older s would work just as well, as would most other GSM phones, i remember seeing a second hand htc hero on ebay for $100, old but i would think that if you just need email and web it would work splendid, maybe would need a new battery tho, but those are not that bad i think.