From my own testing, you do not need to be connected to your Mac via BT or wifi to relay SMS. I have both wifi and BT off on my phone. I can send an sms from my mac, and see it in my phone. Chat history is in sync on both devices. What appears to actually be going on is that the phone is receiving sms then delivering it via iMessage to the mac. I think this is pretty damn cool and means we dont need to have our wifi and bluetooth on 24/7. Now of course, since neither have a cellular radio, the iPad and Mac need to be on wifi. Plus, any call forwarding likely does need WiFi on all devices since a phone call or facetime relay needs far more bandwidth. Its covered in another guide but to make the initial setup work and have the pairing code appear on all devices you need to set your phone and mac to be reachable from both your phone number and apple ID. If you just elect to be reachable by phone number it wont work.