Go here: http://prepaid-phones.t-mobile.com/sim-card. Check your device, and once you know which SIM type you need, click the "Add to Cart" under "Phone".

I literally just did this, so the timing of this post is nice. Even more nice is that they are waiving the $10 SIM card fee right now.

You buy the actual plan after you get the SIM and activate it. I don't know what they charge for activation, if at all.

So it's not available to current T-Mobile customers unless you want to change your number, then?

Move your number to Google voice

Then you can use your unlimited data for calls (if I'm not mistaken)

I used switching to that t-mobile plan as an opportunity to set up google voice. At least now I can cover future number changes.

Port out to another prepaid, then back in.

It's listed on this page (about 2/3rds of the way down):

http://prepaid-phones.t-mobile.com/prepaid-plans

I believe you have to buy the SIM card and then go to this page to pick your plan:

http://prepaid-phones.t-mobile.com/prepaid-activate

They sell it through wal*mart

http://www.walmart.com/ip/Tmobile-30-Wireless-Airtime-Card/1...

Look at "Which plan is right for you" on their pre-paid site: http://prepaid-phones.t-mobile.com/prepaid-plans

I wrote about how to get it.

http://ngokevin.com/blog/tmobile/

You have a typo, "100 minutes of text".