I am not sure.....
You should ask CINCULAR if they can give you 2 Months of FREE unlimited DATA, so that you can develop a pattern of how much DATA you need.....
MANY BOOKIES (Carib, WWTS, CRIS & others) have a special application that you can download to your unit so that you can access their betting sites much quicker....
The thing is your GF may see those icons on your desktop of your treo, but there is probably ways to hide them into a special folder....
The names of the sites you visit, however, I doubt will appear on your bill, unless of course CINGULAR works different....
***** Do not forget, if you are buying the UNIT from EBAY & it is a GSM unit with SIM card, the unit must either be 'unlocked' or 'Branded to CINGULAR'.*****