As of version 2.2.3 your messages can be greater than 160 characters but you'll have to send to fewer recipients. So, if you have 161-320 characters in your message you'll have to reduce your addressee list to 50. If you have 320-480 characters = 33 addressees, etc.
If you try to send again too soon you'll get a force close. If anyone can identify what that timeout period is it would be much appreciated.