Kannel is an open source WAP gateway.  It attempts to provide this
essential part of the WAP infrastructure freely to everyone so that
the market potential for WAP services, both from wireless operators
and specialized service providers, will be realized as efficiently
as possible.

  Kannel also works as an SMS gateway for GSM networks.  Almost all
GSM phones can send and receive SMS messages, so this is a way to
serve many more clients than just those using a new WAP phone.