There is... either purchase a new Sidekick from T-Mobile or purchase one from a friend or an auction website such as eBay or Craigslist.

When I had the T-Mobile To Go service I had purchased a To Go SIM card from eBay-- search for "t-mobile to go starter" and some should come up-- and they include some prepaid time.

When you have your Sidekick and your To Go SIM card put the card in your phone and from what I remember, a screen should pop up asking for you to activate the SIM. You'll be able to call customer service from your Sidekick; just tell them you're trying to activate To Go on a Sidekick and they'll guide you through it and you'll be using your prepaid Sidekick in anywhere from 15 minutes to a few hours (activation times may vary, the longest I've had to wait was about 3 hours when I had got my Sidekick with a regular plan.) Make sure you have your SIM card number and the IMEI number of your Sidekick (*#06# to get it from the main screen) on hand before calling.

The service is a dollar a day for use of data (texting, IM, internet & email) and 15 cents a minute to use it as a phone in additon to the dollar a day. You can purchase refill cards from various places such as 7-11 or Wal-Mart or refill it online with a credit card @ my.t-mobile.com.

Cool. Now you know what there is to know about prepaid Sidekick usage! Yay!!!