Routing problem with Asterisk and SPA3102

Hello, I’m having some problems when I try to generate an auto dial call to the PSTN through a SPA3102. When Asterisk picks up the call file it generates the call to the channel that is going to call to the PSTN, which is in the SPA3102 (A sip peer), as soon as it answers it executes the context that I tell it to execute, but I need to execute the context not when the SIP channel answers, I need to execute when the person in the PSTN answers…

What can I do to do this?

My call file is like this:

Channel: SIP/8900041@ivan_pstn
MaxRetries: 1
RetryTime: 60
WaitTime: 30
Context: default-msg
Extension: s
Priority: 1