Comparing three different phones, the Sidekick, Blackberry and Treo on the Sprint and T-mobile networks. I might add Verizon later.

T-mobile:

Sidekick Unit = $349 ($249 after MIR)
Sidekick Voice = $50 (1000 anytime + unlimited weeknight/end + 40 c/min over)
Sidekick Data = $30 (unlimited)

Blackberry 8700g = $399 ($299 after MIR)
Blackberry Voice = $50 (1000 anytime + unlimited weeknight/end + 40 c/min over)
Blackberry Data = $30 (unlimited)

Sprint/Nextel

Blackberry 7100i = $349 ($199 after MIR)
Blackberry Voice = $30 (200 anytime + unlimited weeknight/end + 10 c/min over)
Blackberry Data = $50 (unlimited)

Treo 650 = $499 ($299 after MIR)
Treo Voice = $30 (200 anytime + unlimited weeknight/end + 10 c/min over)
Treo Data = $15 (unlimited)

Sprint definately has a better voice network than T-mobile. The Treo 650 seems like the best deal if you want to get a PDA phone, however I believe you are forced to use the Sprint “version” of the internet called Sprint Vision.