Is there a limit on the dialup phone number?

["Gary E. Jacobs" <gjacobs@qualcomm.com>]

I'm trying to enter use the MCI worldphone and this means I need to enter a
long number in the form of

1771502727,,,nnnnnnnnnnnnnn,,,nnnnnnnnnn
(MCI Israel     (credit card number)   (modem number)
 Number)

The phone never goes offhook.  I've got an IBM Thinkpad 755CE using the
built-in 144 MWave DSP version 1.1.

If I use 001nnnnnnnnnn it works fine (but costs more).
                (modem number)

The worldphone number works fine if I don't use the modem.

Gary Jacobs
from Israel