As far as i know, most phones do not have dedicated GPS chip. What it does is use the surrounding telco bases to "triangulate" to get a position. Even if one switches data roaming and 3G off, the phone will still use 2G to get its position. The question then becomes - is this chargeable when u are overseas, and if it is then u could be getting a "huge" roaming bill when u return home.
Hopefully someone can come in and clarify