Maybe you meant to create ppp interface that can be used to actually call-in somewhere or use to connect via 3G modem? If so, please check appropriate section on wiki.mikrotik.com
Are you serious? I know what PPTP is, and how it works, and what I want to achieve with it. I even referenced an RFC describing how the “phone number” is used in PPTP
My guess is that you are configuring a pptp client and want the connect-to parameter. Perhaps the wiki at http://wiki.mikrotik.com/wiki/Manual:Interface/PPTP would be of help.
If this is not the case, might I suggest a more detailed description of your application and problem?