I can't think of any reason why the higher post paid plan would be better. If I remember correctly, the OLD postpaid data and text only plan for SKs was like 30 dollars but they upped it. There's really no benefit at all.
If you want SK data only, then go with the prepaid.
I have them both. What I find is that with the prepaid plan if you are only using the Sidekick, as long as you get the web guard on it, it is a better value than the "new" priced 54.99 deal. On the other hand, if you sometimes like to send MMS, you are unable to do this with the prepaid plan as they turn off the regular data service. This meaning if I were to put my sim card in another phone, I would be unable to view T-zones, send MMS or use instant messaging. With the postpaid version, you are able to use all aspects of data. I am not saying I could browse the web as I would with the sidekick, but will be able to use those things listed above with no problem.
I also worry about data roaming with the postpaid version. There is absolutely nothing to worry about with prepaid. If you are unable to roam, it won't work. With postpaid, there is a possibility of perhaps getting charged for data roaming. I don't have experience with that because it hasn't happened to me, but you just never know. Also, I have the grandfathered version add-on for 19.99, which everything is unlimited. I think it is crazy to pay 34.99 for this service considering I am unable to browse the web on any other phone. Why is it with this plan you can not web browse but with the other data plans such as the Blackberry service and Windows Mobile data I can browse with any other phone?
Anyway, there are advantages and disadvantages to every plan. Personally, if you don't use your sidekick for calls and don't want a contract, and don't prefer to use another phone to web browse, the prepaid plan is best. I have the 19.99 calling plan with MyFaves so for me, paying the extra 10.00 for a few calling minutes is perfect for me!!!
Thanks for the replies guys. Yeah screw the postpaid plan, I'm getting the sidekick prepaid. Eventually I plan on actually getting a voice plan and will get the sidekick add-on, but for now, $1 a day works for me