I call this plan the "Very flexible if you know how to use it plan" accordingly.
All the other plans charge you a daily fee of $1 to $3 everytime you use the phone. The $.25 Simple Plan does not charge you for daily fee's so that mean's you can technically use your phone every day of the month (For text messages, Internet uses, and Incoming + Outgoing calls with Skype)
So all I need most from a cellphone plan is text messages since that's what I do most with it.
I get 1000 text blocks at a time for $10 and I use about 1500 texts every month which brings my total cost for text for the month to $15.
I always keep an extra $5 on my account for incoming calls that I need to take and usually only use a minute ($.25) before I call them back with skype on my iPhone.
How to integrate Skype into your iPhone on a GoPhone Plan:
Using Skype to make a 5 minute call cost you roughly $1 using AT&T's EDGE network and yes you can use Skypr just fine on EDGE as long as you have the VOIPover3G mod from Cydia.
So $20 100mb data package let's you in turn use Skype to use 500 minutes on your phone. I barely use minutes and also use EDGE for browsing the web and 100mb is plenty for a few months for me. I just add an extra 1 mb every month for $5 so I can keep the rest of my unused MBs since they will simply roll over.