i had a sidekick 2 and then traded it in for the sk3.
i ended up cancelling my service with t-mobile because i was very unhappy not only with the phone (it would restart and freeze sometimes), but whenever i needed to text or call someone.. i didn't have freakin service!
so .. i went back to verizon.. got my motorola q has not froze on me yet
(i've had it for about 5 months now).. and i use it for texting etc.. but the majority of my family and friends have verizon so that's why i went back as well.
you can always go on
www.amazon.com and check out the reviews.. that's what i did when i was trying to select the sidekick 3 or the mda.. but now i got the motorola q and am very happy with it despite some of the things they said (it freezes, i believe that was when it first came out and they fixed it).
good luck on whatever you decide!