Dialplan: s vs. _X


I have problems with incomming connections. I figured out that for some accounts i need dialplan which uses ‘s’ as phone number:
exten => s,1,Answer
exten => s,2,Playback(tt-monkeys)
exten => s,3,Hangup

and for other account ‘_X.’ like this:
exten => _X.,1,Answer
exten => _X.,2,Playback(tt-monkeys)
exten => _X.,3,Hangup

Why ? Why this difference exists ?


s is a special extensions which means start here, if you had a zap trunk it has to start with s. “_X.” means any extension dialed.