Yes, you can. Although as analog fax machines speak a different language as modern IP phone systems, it is possible to integrate a fax into an VoIP network. The T.38 protocol is it, what allows this feature. It is able to send fax data “packages” via a data network, if the chosen provider supports this function. Therefor it is necessary to convert the convetional fax protocol (T.30) into T.38. Either the used fax machine itself is able to use T.38, or it is necessary to use a gateway, which translates the T.30 into T.38 and back. With this two options it is possible to integrate the analog fax directly into the PBX. This is called FoIP (Fax over IP). Beside it is possible to connect the analog fax with an analog port and run it parallel to the VoIP network.