extentions.conf 

[callme]
exten => s,1,Wait(3)
exten => s,2,TxFax(${FAXFILE}|caller)


Channel: Zap/1/604xxxxxxx
 MaxRetries: 2
 RetryTime: 60
 WaitTime: 30
 Context: callme
 Extension: 800 
 Priority: 2 


What is the extnetion part for?