If the PDA has wifi, then you could use one of the 3G-to-wifi bridge devices. I use this one which allows any number of laptops, computers, PDAs to share the 3G connection. Check your 'dongle' is compatible on the list at the bottom...
however I only want to use the pda on the boat, so was wondering if I could take the sim card out the dongle and bung it in a blue tooth phone and use the phone as access? .. and if so is there a partic of phone type I need ?
3 Skypephone S2 will work for 3 mobile broadband sim and has bluetooth. I think about £40 at the moment. And you can install opera mini to use the phone as an internet browser.
Check the internet forums or compatibility list for your particular PDA. Most all bluetooth capable phones will work just fine. I use an old Orange Sony Ericsson k610i which does just fine. Most mid-range phones in the last 3-4 years should be more than capable.
However, you will make your life much easier by choosing something where the settings are well described for your model of PDA and phone. The APN setup, modem initialisation and dialling strings can get quite technical. Other phones make the whole process simple by hiding all that from you and your PDA, just presenting themselves as a Bluetooth network access point. Google is your friend here.