That sounds like BlackBerry BIS. All map apps will use BIS data to download maps on the fly as they're needed. BlackBerrys generally do not cache maps to use later.
Email pushed onto your BB is BIS data. MMS messages are as well, but some carriers charge a fee for each MMS or SMS message. Not for email. Text (SMS) messages go over the cellular radio connection just like phone calls and use no data at all.
Here's a little primer on using a BlackBerry without a BlackBerry data plan. It should answer some questions about what is BB data and what's not: How to use BlackBerry on Generic Data Plan - BlackBerryFAQ