6/30/11 Due to Virgin Mobile closing an account of ours that had funds in it, that should have been active for 365 days we can NOT recommend using Virgin Mobile at this time!
6.27.13: WE ALSO HAVE ISSUES VIRGIN MOBILE TECH SUPPORT AT THE PRESENT TIME, AND AGAIN ARE NOT RECOMMENDING THEM - ALSO, THEY NO LONGER OFFER PER-MINUTE PLANS, SO THIS POST IS OUTDATED, AND NO LONGER RELEVANT.
I have always recommended the Net 10 LG300 for a throw away phone. The reason being that they cost $25 to $30, depending on if they are on sale or not, and comes with 300 minutes, that are good for upto 90 days. This phone and its 300 minutes plan is still good for low usage, where you do not expect to use all of the minutes in a single month, BUT if you need to use more minutes within a single month, then I have found an even cheaper alternitive.
Virgin mobile has always had several phone models in the $10 range. Currently the kyocera TNT (flip) and JAX (candybar) phones are $10 each, and with a $20 paylo plan you will have 400 minutes to use to talk.
So for the same $30 you can have a Net 10 phone for 60 days and 300 minutes (with 10c additional minutes, if you actually add money to your throw away), or a Virgin mobile phone with 400 minutes (for 30 days, with 5c additional minutes.)