The V.110 protocol is often used when a mobile phone (GSM) connects to the ISDN in order to access a data service, such as a WAP gateway.

This conversion is handled transparently by the data gateway that connects the GSM network to the ISDN network.

Some GSM to ISDN gateways convert the call into a low speed modem format. Which format is used depends on the internetworking function chosen by the two network operators. The user has no control over this. Handling both types of call transparently is a challenge for the recipient of the call.

 For voice calls between the GSM and ISDN networks, a different conversion is performed to convert the GSM format for voice calls to the ISDN format for voice calls.