I'm aware of quite a few people who use the 1000HX for packet
   radio - as the 1000EX is a very similar computer, the
   differences should be small. Unfortunately, I don't have their
   names/addresses handy :-/ You can purchase a serial board for
   the EX from: DCS Industries *or PC Enterprises as well as from
   your local Radio Shack. I believe its approximately the same
   price for all of them. I will e-mail the Tandy 1000 FAQ and you
   can find the addresses for DCS Industries and PC Enterprises in
   it.