I am not 100% sure but S700i was announced around March 2004 and only supports Bluetooth Version v1.1 vs. W700i announced on Apr 2006 supporting Bluetooth Version 2.0.
You may need to call Sony to find out if the v1.1 on your phone truly supports Bluetooth Serial Port Profile (aka SPP), which is required to work with any Bluetooth GPS receiver.
Also, the Java version on your S700i may be an older version. The Java run time on W700i is based on Java MIDP 2.0. You should try to download a copy of Google Maps for Mobile ant see if it installs and loads okay.
Good luck.