What do you mean your iMessage won't activate? Can you provide any details?
Try following the steps here:
After each step, toggle iMessage and FaceTime off and then on again in Settings > Messages and Settings > FaceTime.
- Update to the latest version of iOS.
- Ensure that you have an active Internet connection. Check your Wi-Fi network using standard Wi-Fi network troubleshooting.
- If you receive an error when signing in to your Apple ID, visit myinfo.apple.com, sign in to your account, and ensure that the primary email address has been verified.
- Ensure that FaceTime has not been restricted: Settings > General > Restrictions > FaceTime.
- In Settings > General > Date & Time, ensure that Set Automatically is on. If Set Automatically is on, but the incorrect time zone is displayed, turn Set Automatically off and then choose the correct time zone, date, and time. Then turn Set Automatically on again.
- Enable iMessage and FaceTime while connected to another Wi-Fi network in a different location.
- If "Waiting for Activation" is displayed, leave FaceTime and iMessage enabled for 24 hours. Toggling FaceTime or iMessage off and on will cause the registration process to start over.
After each step, toggle FaceTime and iMessage off and then on in Settings > Messages and Settings > FaceTime.
- Update to the latest version of iOS.
- Verify that you are connected to a cellular network and can send SMS messages. You need a valid SMS messaging plan to activate FaceTime.
- Ensure that FaceTime has not been restricted: Settings > General > Restrictions > FaceTime.
- In Settings > General > Date & Time, ensure that Set Automatically is on. If Set Automatically is on, but the incorrect time zone is displayed, turn Set Automatically off and then choose the correct time zone, date, and time. Then turn Set Automatically on again.
- Contact your carrier to verify that there are no restrictions on text messages. Blocks on text messaging will prevent iMessage and FaceTime registration.
- If you are unable to activate iMessage or FaceTime on a device after remote wiping it, wait at least 24 hours and try again.
- If "Waiting for Activation" is displayed, leave FaceTime and iMessage enabled for 24 hours. Toggling FaceTime or iMessage off and on will cause the registration process to start over.
iOS: Troubleshooting FaceTime and iMessage Activation
http://support.apple.com/kb/TS4268
As for messages going to your old phone... are they replying to your Apple ID? If you're not signed into your Apple ID on your iPhone 5 then you won't get the messages.