Replies to text messages sent from iOS arrive at OS X only
If their reply is in blue, it's an iMessage, and you disabled iMessage, so it won't come through. If the message is in green it is an SMS, which will always come through. The only way around it is to disable iMessage on all your devices so that your friends' iPhones don't pick you up as iMessage-enabled contact and hopefully send you SMS instead of iMessage. If the iMessage didn't went through they can touch and hold the blue message and tap "Send as text message" to send as SMS.

So the solutions are to enable or disable iMessage on all your devices. I'll go with enable, because you have nothing to lose and makes life easier for everyone and yourself.

If you really don't want to enable iMessage on your phone, at least narrow down the emails/numbers where one can get to you. (if that is the reason why you don't want iMsg??)