Of course, those TI calculators were a little on the slow side. The intarweb comes to the rescue: with just a little overclocking know how, you can bring the older machines up to a blazing 12MHz and the top-line beasties all the way up to 20MHz!
Curently, the TI-81, TI-82, TI-83, TI-85, TI-86, TI-89, TI-92,a nd TI-92 Plus can be accelerated. The 81, 85 and 86 can be accelerated to approximately 2-3x their normal speed, about 18 MHz. The TI-82 and TI-83 can also be accelerated to about 1.5-2x normal speed. They only about double their speed to around 12 MHz. The TI-89 and 92 can be accelerated to around 20 MHz!Link (via Make Blog)
Update: Martin sez, "I believe you are confusing TI with the HP48 series of calculators by Hewlett-Packard. I'm not aware of any TI with an infrared feature, probably because of the trouble HP has had with theirs. Here's some documentation on HP's IR port. On the other hand, there is a hack to add an IR port to TI calculators here."