Hello!
You have to define T62 service in HLR for subscriber. Teleservice 62, automatic facsimile group 3, is an automatic fax service where the receiver has a separate MSISDN for the fax service and all calls to this number are purely facsimile calls. You also have the corresponding pool in A-interface which allows data calls.
Then you connect mobile to PC and send fax. You can use native Windows fax service or some other software such e.g. VentaFAX.
I want to mention that the newest Nokia mobiles do not have fax option. The last model which supports fax for sure is nokia 6310 , at least I used this model.