You have two options:
1) An internal cellular modem. This is more expensive. However, Fujitsu makes
a mobile phone with a datalink option.
2) Use a data jack with any existing Hayes-compatible modems. The data
jack serves as an gateway and does not interfere with the phone or the
modem. It is independent to the modem baud rate. Data jacks costs
about $150 and are available from Cellab in Canoga Park, CA.
You might want to try the phone book in your area for distributors of these
products. If you cannot find any information in your area, try the
following distributors in Northern California: CelluTel of Palo Alto and
Mobile Land in Fremont.
To locate a vendor's address and phone numbers, use the vendor name as a
search string.