My BT device user guide tells the maximum number of phone book entries may be as low as 250 or 650 on some operating units. It should still not restart without any contacts downloaded, that sounds like a bug.
1 number = 1 number. It puts in different names for each number a contact has by adding /W /M or /H (work , mobile, home).
The 250 limit applies to D2B systems (and its 250 minus size of SIM, i.e if the SIM can hold 200 names. 200 slots get used even if empty). I don't know for sure the limit on the new ones, but as DieselBenz says the SAP cradle manual has some figures in it.
I'm interested to know what Cixi finds if he deletes a whole bunch of contacts.