The invention discloses a user service switch 
system, a device and a method, which include: a packet 
access network, a mobile switching centre, a 
user device, a packet access unit, and a possible circuit domain. The packet access unit is used for ensuring the signaling path between the packet 
access network in the packet domain and the mobile switching centre in circuit domain, and the load between the management 
user device and the mobile switching centre; the packet 
access network is used for handling the switch of the circuit domain 
overlay area or the packet domain 
overlay area; the circuit domain assess network is used for handling the switch of the circuit domain 
overlay area or the packet domain overlay area; the mobile switching centre is used for handling the switch from the packet access network or to the destination of packet access network. The invention ensures the use can carry out the switches of packet overlay area or circuit domain overlay area as destination area or 
source area when calling, under the control of MSC, which is good for the operator to sufficiently use the packet network overlay to provide more continuous services for users, thereby improving the use efficiency of network.