All trunks are busy now,please try your call again later

Hi all,

I am having issues on my freepbx asterisk box Version 2.0.1

I make internal calls on extensions configured ie extension 367 can
call extension 368 etc

But each time i try to make calls outside the extension ie calling a
GSM or an external line ,i always hear this response “all trunk calls
are busy please try your call again later”

Please how can i resolve this problem .

I will appreciate your response.

Best Regards