from the SailMail site:
This is Icom's original HF marine radio. This radio has a number of disadvantages for use with digital communications.
There is no accessory jack with the necessary AF input, AF output, and PTT signals. The addition of an accessory jack will require you to have a radio technician modify the radio. Most radio technicians will (sensibly) refuse to do this modification because they feel that it is pointless to work on such an old radio. If you do decide to get the modifications done be sure to get the price quoted in advance, and then reconsider just replacing the radio.
Once modified, the M700 still is not ideal. It is only capable of about 50 watts continuous output.
I am a licensed tech and I would be very leery of modifying a type certified radio without the manufacturer's blessing.