It depends on the modem Internal/external and the modem's software.
If you mean an internal modem then go to www.lenovo.com and download a manual for your ThinkPad.
If external read the modem's manual.
If any of this doesn't make sense or you need to know more post a NEW question (this will look closed) with LOTS more information about what you are trying to do.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix notebooks/laptop pcs.