This show hasn't come up in my podcast rotation yet, but wanted to throw in my 2c.

I run a TMO prepaid SIM in my G1 (Cyanogenmod 6.1), but use something like 15mins of phone a month.  

Everything else is wifi, automated with Tasker.  The TMO sim has an advantage that you can get a 24hr data daypass for $1.50 if you find yourself somewhere with no wifi and a desperate need for connectivity.  Happens to me about once every two months or so.  