Note there is no way to disable call-waiting on the receiving end. Back to top of page I have a high speed modem that only connects at low speeds or doesn't connect at all. The first thing to check for is that the modem you are calling is at least as fast as yours. The fastest speed that you can connect at will be dictated by the slower modem. Sometimes you will just get a bad connection.
Computers have that problem too sometimes.
Hang up and try again. Make sure your software is set to the rate at which you want to connect. The modem will not connect any faster than it's configuration allows. It may be difficult to connect at high rates because of phone line quality in your area, or across a particular piece of phone equipment. Also, some modems are just higher quality and are better able to get high rate connections in spite of other conditions.