These apps have saved me so much phone credit that I just don't know why I need a $49 cap anymore!
Voice Calling - Skype
Best to use at home with a wifi connection. Prior to having iPhones, I had to sneak out and grab the phone and quickly answer it as soon as Yi rang me to avoid waking up the whole house. Quite the pain...otherwise we would just call each other on mobile and talk for awhile. With the phone my arm often got tired and I had to switch arms to stop them from going numb. With the mobile I had loudspeaker but it burned lots of credit.
Now since we both have iPhones, we just lie in bed, with our headsets on, and talk on Skype for virtually no cost! WIN!
Messaging - Ping
I've already done a post on this, but this app seriously saves you so much credit money. Yi and I havent texted each other via SMS since we started using Ping! It just uses a tiny tiny amount of your 3G data to send text messages. Even with my 250mb/month data plan it is more than enough to send at least 20 pings a day. WIN!
Now the only problem we're having is how to spend all this excess credit we're building up!!