assumptions
well... if they are PAGING us... that might mean that they had received one of our spamming signals that we have been graciously trashing our system with...
Now here comes my assumtion...
if they got our message and are trying to talk to us, it would make me think that THEY also went through the trouble of Decoding it... and if they are sending a message back that means that they decoded it to something that they believe is close enough to the original message...
So I would initially try to decode it with wahtever coding algorithms we have been using for any signal to satellites and radio... if that doesn't work.. well.. then they got their decoding wrong ;) and it's all their fault!