Techniques for initiating and, if desired, modifying location services for Secure User Plane Location (SUPL) and other location architectures are described. To initiate SUPL service, a SUPL Location Platform (SLP) transmits a SUPL initial session message applicable to any service request to a SUPL enabled terminal (SET) and receives in response the service capabilities of the SET. The SLP selects and requests service from the SET consistent with the service capabilities of the SET. The SET may initiate SUPL service by requesting the service capabilities of the SLP. The SET selects and requests service from the SLP that is consistent with the service capabilities received from the SLP. The SET and SLP communicate to determine a position estimate for the SET. The service may be modified before or while communicating between the SET and the SLP to determine a position estimate for the SET.