How do you stop sms messages automatically being sent to an email address instead of a phone number?

Question

I have noticed that sometimes (particularly when sending an sms to multiple people) my iphone 4s will send the message to peoples email addresses. This happens despite there being a phone number listed on the contact. You would have thought that an sms would automatically send to a phone number if there is one available for the contact, but instead it is sending the sms to an email address without warning. This results in me being charged for an mms and the recipient not recieving the text at their phone number. It happens when sending messages to both iphone users and non iphone users.
Does anyone know a way of fixing this?

Answer 1

I think its fixed. I had to sign iMessages in on my Apple ID, but then deselect my email addresses to make it behave the way it should. Now if I could get iMessage to only send response alerts to the last device I used, instead of late night texts going to every device I own in the house and waking everyone up.
For some reason, the free iCloud address I automatically received (when Apple was trying to force people to leave Mac.com) is "hardwired" into iMessage. People were also getting texts from that address even though I was on my phone. I tried to delete it but iOS tells me I can't. I don't use that address, I won't ever use it, too bad I can't make it go away.