iphone plan?

[DavidKLe562]

hi im new to this forum and had a question to ask.. I recently purchased a iphone and had a sidekick LX before that with a sidekick plan which i was paying 20 dollars for and when i put the sim into the iphone everything works fine besides the internet. ive asked friends and stuff and they said if i upgrade my sidekick plan to the newer one which is 35 dollars a month instead of 20 the internet will work again but then again i was wondering what were the previous phone of other people BEFORE having an iphone and how did they get internet to work? Because i want to just upgrade my tmobile line and just add internet and still have the sidekick line but i can't do that and i need to change my phone to something else in order to upgrade to normal internet.

Thanks