AirPort software version 2.0.4 and later allows an AirPort Base Station to accept incoming dial-up, PPP connections. This allows remote access to the base station and the computers on the AirPort wireless and wired network.
If you connect to the base station from a V.90 modem, the best speed you can expect is a V.34 speed of 33.6 Kbps. This is a limitation of the V.90 standard and does not indicate any issue with your modem or base station. Although the V.90 protocol allows connection speeds of up to 56 Kbps, this maximum speed cannot be achieved between two consumer-grade modems. Specialized equipment, typically owned by Internet service providers, is required at the receiving end to enable maximum speed.
Note: The incoming connection feature can be activated only from Mac OS X computers. Only the AirPort Base Station (Dual Ethernet) can accept incoming calls.