Your modem listens for a dial tone before it dials. If the tone is too quiet, it will fail with the Carrier Signal message. If you go into your modem driver you will find a option not to wait for a dial tone before dialling. Check that option.
If there are misdialling problems after this, precede the number that the modem is dialling with a comma. This inserts a short pause (I think half a second) which is enough for the dial tone to appear before the modem starts dialling.