The webConnect data plan will cost $59.99 a month for 5GB of usage with unlimited Hot Spot access. Once over the 5GB limit, T-Mobile will charge you 20 cents per MB with no voice service allowed. While 5GB might seem small, using them you could visit 35,000 web pages or send 1,700,000 1 page emails with no attachments. 5GB would also allow you to download 1,300 songs that are 3 minutes in length. No matter what combination of browsing, downloading or emailing you do, it seems like the plan gives you enough data to cover 1 months' usage.
source: CellPhone Signal