Hi Epage. I tried messing with the code a bit to give you an idea of what I think is "thumb friendly" and also would like for other users to comment on it. Here is my contacts tab. I stretched the rows to the "optomial" size. I was unable to figure out how to change the font to fit the scale, but you get the idea. The size can be accomplished in the recent view as well. Simply shorten down the time like you had before, leave them small, and the contact name large. Instead of showing the number, clicking the name brings up the contact info with all numbers available. (probably a pain to do)
One other idea. In messages view, when you click on a message to reply, we are forced to click the sms button in order to start replying to the message. Can you instead have the reply window there to eliminate a step. You can leave the sms button there in order to send the sms, and include a Call button or something similar incase you wanted to simply call the user. I have also taken the liberty in doing a mock up of how I envision the app as it moves forward photo support linked to the saved address book would be such a spiffy touch