You don't state what type of "mobile" your friend has. Some BT enabled phones can accept Contact information from a fellow BT item. To facilitate - both devices have to have BT enabled and then they have to be paired to one another. You'll probably need to know at least one if not both of the devices "security" or BT access code. Typically, for the Tungsten T it was 0000 as I remember but refer to the manual for certain.
Once the "handshake" is made then the two devices can talk to one another. This handshake though may not necessarily allow andexchange of data. If your T is talking to a phone - it's usually only going to be either to use the phone as a modem and hence surf the web or to be able to dial the phone via the Contact features of the T. Data exchange is not normally possible in BT mode.
If your "mobile" is a Nokia phone and you wish to send it contact information - most of the late model Nokia's that have IR can accept contact information. The Nokia or other IR phone would have to have the IR enabled (it's normally off for battery conservation) and then you could simply "beam" the contact information to the phone.
Without the specific devices being named - the above is just hearsay.