The Java ME Location API says it supports:
Quite a number of phones support this API (JSR179). However, some phones don't have an inbuilt GPS module, is it still possible to use this API to obtain the phone's current location?
Mobile Network based positioning.
The security settings will control if you can access this, the service provider may also make a charge.
From my very limited experience of J2ME, you can set the phone to not allow an app access to private data (such as location) and to charged for services (such as location) - you can also set it to popup a request for the user to authorize it.
J2ME is pretty well designed to gracefully fall back to whats available and hide a lot of the details.
Yes, some GPSless S60s (e.g. N70) give location through this API when used with an external GPS device attached via Bluetooth. Others may possibly give you approximate location using CellID.