At present, the international communication standard organizations take the network based on IMS as the evolution target of the future voice switch network, because the future IMS will coexists with the network based on CS for a long time, the problem of route selection and decision occurs when SIP user calls E.164 user in IMS. Therefore, this paper gives 3 route solutions when SIP user calls E.164 user in IMS: S-CSCF self routing solution, ENUM querying decision solution, and the BGCF routing selection solution, and gives the compare analyze and application suggestion at the same time.