Hello
How about other recipients? Do everybody else you send messages to receive them ok? Is you friend in Indiana receive messages from others? I would start with a phone restart on both ends, if your phone has a removable battery, remove the battery for a minute and then restart, if not, just power off your device for a minute and restart. Ask your friend to do the same. If that doesn't work you might want to go ahead and replace your SIM card, any corporate AT&T store can provide one for free.
Thanks,
Dmitriy