A PSTN service control point including multiple subsystems, a memory storing inbound SS7 messages and a SS7 module which internally routes outbound messages directed to the same point code. On receipt of an inbound SS7 message, a SS7 controller stores the complete message in the memory. The SS7 module routes the message to a first subsystem which processes the message and adds new information to the stored message in memory. If the first subsystem needs to collaborate with a second subsystem, it routes the SS7 message through the SS7 module which checks the outgoing message point code. If the destination point code matches the first subsystem point code, the SS7 module treats the message as an inbound message and routes it internally to the second subsystem.