The speed that a modem can transmit data through telephone lines is the most important consideration when buying a modem. Modem standards ensure that modems made by different manufacturers can communicate with each other. Faster modems cost more, but will save you time and money in the long run. When transferring files, faster modems take less time and save you money on long distance and online service charges. Modems must use the same speed when exchanging data. A fast modem can talk to a slower modem, but they will communicate at the slower speed.