With sprint your pretty much limited to WinMo and Palm smart phones. BlackBerrys are awesome phones but I'd only recommend the Storm for reading, rumor has it. Also the sprint now has the Nexus One an Andrioid phone which has two reading clients for ePUB and for eReader.
Of course you can bypass some of the extra charges ATT & Verizon charge by using tools like Google Voice and Google Maps. If you bought a BB you can use BlackBerry's Maps.
Google Voice gives you unlimited text messages since it uses your data plan to transfer your text.
Of course this solution does not work with the iPhone.
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