computer first aid
Before your modem software dials a phone number, it initialises the modem by sending it a series (string) of commands, which configure the modem's options for things like error correction, data compression, flow control, and many other parameters.
The important thing about modem initialisation strings is that having the right one often makes the difference between connecting and not as they are fairly specific to each modem.
There are numerous sites on the internet where you can locate the correct initialisation string for your modem, however you must find the exact string for your specific brand and model of modem, otherwise your modem may not work at all.
Your Internet Service Provide can suggest a "generic" modem string, however there are literally hundreds of possible modem strings, so you will get the best results from the string that is specifically for your brand and modem of modem.
Some modem string reference sites:
http://www.modemhelp.net/stringlist.shtml
http://modems.rosenet.net/init