You left off Virgin Mobile from your list. They have some plans that feature unlimited texting. http://www.prepaidreviews.com/virginmobile.html

To compare all of the providers you have listed side by side (3 at a time) you can go to http://www.prepaidreviews.com/compare/

That is the best resource online for prepaid cell phone information.

For Verizon Inpulse (Prepay) Customers $20/month for Unlimited Messaging to anyone on any network in the U.S

http://www.verizonwireless.com:80/b2c/store/controller?item=prepayItem&action=viewPrepayOverview

Dial *611, select Additional Options, then select the option for calling plans and features and follow the prompts for changing optional features.