The Byte-Back MD-2B is an excellent choice for a modem for the Timex Sinclair computers. It plugs right onto the back of the 1000, 1500, and ZX81 computers. There is an extra kit you can buy that adapts the MD-2B to the TS 2068. It is an additional $19.95.
Byte-Back has been making modems for the Timex Sinclair 1000/ZX81 for over a year, and their newest modem is great. It even beats the Timex 2050 modem. You may think not, because you can get the 2050 modem for only $119.95, but the Byte-Back modem includes a down/uploading program and a free serial printer port, both of which the 2050 does not have (the downloading program will cost $19.95 for the 2050 if, and when, it comes out, so that alone brings the price right up to the MD-2B). The MD-2B does not have auto dial/answer like the 2050, and they are not really that important. Auto answer is not needed at all, since if you leave the computer on, it will answer the phone every time it rings, and that can be a nuisance. I also think the MD-2B has a much better terminal program for the 1000. With the MD-2B’s terminal program (Z-COMM), you can send and see an apostrophe, brackets, the “#” sign, and the “@” sign, all of which just show up as inverse grey spaces on the 2050’s terminal program for the 2050, and they can’t be sent (obviously).