Have you tried turning your phone off and back on again?
Also be sure to check that you haven't blocked any of these contacts by using Extreme Text Messaging
Are you able to receive and place calls to these numbers?
Sometimes there might be a delay for text message to be received by the new number.
If you friends are using iphone, you can ask them to turn off iMessage and try again.
And also your friend may need to create new contact instead of updating phone number for old contact.