You need the Ericsson data adaptor for the T68i. This plugs into a type 2 PCMCIA slot so if your PDA has one of these, it will work.
As for sending and receiving free....no can do! The fact you are using a cellular phone means that the data has to be sent at 9600 as a data call, and unless you have a freefone number to access (and most cellular companies charge for Freefone calls, and data is ALWAYS charged for...they bill you per Mb!!!) then IP address has nothing whatsoever to do with it! I have used a cellular to access AOL via an 0800 number but have had to use my off-peak free minutes because on the majority of networks, calls to a freefone number from a cellular are NOT free...you still have to pay for the 'cellular' part of the call!!!. Luckily, I get 600 free minutes per month with my tarif (Vodafone Off-Peak 600+50 SMS...?12.99 per month!)