The Next-Generation Network (NGN) has Application Network Interfaces (ANIs) by which 3rd party application services are easily created. For session-control ANI (for example, "makeCallSession" of the Parlay-X), Application Server (AS) functions process a call using three SIP methods (REFER method, 3rd Party Call Control (3PCC) method, Media Bridge method). We propose a SIP method escalation algorithm where each escalation level corresponds to the SIP protocol capabilities a terminal has. We evaluate the proposed algorithm from the viewpoints of resource consumption and session connecting delay, and performed research on issues regarding commercial use. The results are expected to contribute to the future Service Delivery Platform (SDP) or Proactive network Provider Participation for P2P (P4P).