A technique for reliable passage of handshaking information between a cellular modem and a land modem. Instead of bare transmission over a voice channel connection highly susceptible to signal fading and dropout, the initial modem handshaking exchange is instead FSK-encoded and broadcast using a network data signalling methodology already used to reliably pass signalling information between the base and registered mobiles. Automatic retransmission request signalling and transmission redundancy may be implemented to insure successful receipt at the receiving end of the radio link. Once received and verified, handshaking information is decoded and delivered to the destination modem in the appropriate format along cleaner fixed pathways. Reliable handshaking operations are contemplated whether the destination modem is a cellular modem registered in auto-answer mode (land-originated data call), or a land modem (mobile-originated data call). Backwards compatibility with non-compatible cellular fixed-ends or mobiles is maintained through extensive use of active acknowledgment messaging and software timed transactions.