My initial thought was to use the prefixes for model of iPhone, but that seems to counteract my original plan of merging all iPhone topics into. Just because someone asks a questions about an iPhone 4S, does not mean it's not relevant to all iPhone users. By having users select a thread prefix based on model, it might deter non-iPhone 4S owners from taking part in the conversation. Plus, these prefixes wouldn't be very helpful from a forum global perspective.
So, I'm looking for any suggestions on how to best implement them. Thoughts?