No, with dial-up service, the ISP does not need to limit
connection speed. The condition of the phone line you are using
(and the connection path to the ISP's answering modems) is usually
the limiting factor, over which you have little or no control. If
you are getting 40K, then your V.92 modem is probably doing the
best it can under those conditions.

Some reading at http://modemsite.com/56k/what56.asp may help you
understand this.

--reed

The speed is determined by the two modems, not by ISP policy. During
the "training" phase, the modems at both ends test the phone line
(frequency response, etc) and estimate the optimal connect speed for
the detected line conditions. These are the sounds you hear
immediately after dialling and just before login. In your case the
modems are starting out with a connect speed of 40000bps. This speed
may increase or decrease during your dialup session if line conditions
change. It could be that you are on a long line, or maybe there is
some other impairment. In any case 40Kbps is not too bad. IME people
rarely achieve better than 46667bps.

- Franc Zabkar