My iPhone can't text friend's Android, but my wife's iPhone can A friend of mine just switched from iPhone to Android.  He can text me without any problem, but I can't text him at all. I have tried everything I can think of but no message will ever reach him.  They are of course transmitting as SMS since he is no longer on iMessage.

The strange part is, my wife's iPhone (4s running iOS 6) can text him perfectly fine, no problem at all, so whatever is happening seems to be on my end.

Any suggestions on how I can sort this?
This occurs because Apple still believes the phone number is using iPhone, but it can vary from device to device whether this impacts sending and receiving messages to that number (and how long it takes for that to resolve).

The quickest way to resolve it is for your friend to read the Apple support article Deregister iMessage. The deregister process can be done from the old iPhone (if it's still available) or online. It still may take a few hours for all Apple devices to recognize the number no longer uses iMessage, but it could take much longer without completing the deregister process.