I get a $185 monthly bill from AT&T for data & voice usage on the two iPhones my wife and I use. I miss Cricket. I have no complaints about the quality of service I receive from AT&T. But, since I work from my home office, I use my Google Voice account to send and receive free calls, voicemails and text messages. Naturally, I learned I could do this on my iPhone as well with a variety of apps. This also means if I could obtain a data only plan for, say, $35 per phone. Allowing me to eliminate my AT&T plan and save $115 a month! So; I've created a series of comparison charts to identify the best possible alternative to the plans and apps major carriers are currently offering. Note: Google Voice does not currently support picture messaging (including sending recorded videos).   Apps "NT" means not tested. "X" means they are a supported feature. Lastly, this was tested with a Google Voice number associated with a Google Apps account as well as with a GMail associated account.

  Notes

• Google Voice - Due to contractual restraints with Apple, Google was required to cripple their application by forcing it to route the call through the carrier (thus using your minutes). So this application is simply useless for our purposes.
• GWhizz - This appears to be a glorified browser that is dedicated to displaying Google Apps and a few extra features.
• Talkatone - Calls have a subtle static, and .25 to 1.0 second delay when talking (though I may have only noticed the delay because I was listening for it).
  • Update: If you check the message on any device beside the iPhone then your iPhone will leave the Push Notification remains on the screen. So you have to constantly go back and forth to clear the screen. This should clear itself once the message has been read (though that may be a limitation of the iOS not Talkatone to be fair.
  • Update: Also, when you reply on a device or application beside Talkatone, the response doesn't appear in Talkatone. So if I reply to a text on my desktop, then get in my car and continue the conversation my earlier response isn't on Talkatone. So it's not receiving a real time transcript.
  • Update: There doesn't appear to be an "Add to Existing Contact" option.
• GV Connect - Another weakness this application has is that it requires an additional VoiP app to actually place calls. So when you make a call, it opens the other app to dial and place the call. Then when the call has ended it switches back to GV Connect. Also, when sending a text message instead of the traditional reply box at the bottom of the screen it pulls up an entirely new page where you have to enter the reply, preventing you from seeing previous messages.

Carriers

• AT&T presumably offers a prepaid $20 a month data only plan, instructions to set this up can be found here. This method doesn't require you to jailbreak your iPhone.
• T-Mobile offers a contractually bound data only plan for $25 a month (last I checked). This method does require you to jailbreak your iPhone

  In my opinion, Talkatone is the champion because it offers functioning VoiP, messaging and a variety of settings so it can compete with the native iPhone apps. As I mentioned though, it has it's weaknesses, but considering the $100+ a month savings: I can live with it for now.