Is one sip trunk enough for in and out calling at the same time

i have one SIP trunk for incoming calls to FreePBX, can the caller call to FreePBX through this SIp trunk and make call to outside by the same trunk?

This is a question for your SIP provider.

If you have the trunk already why not just try it?

thanks for reply, actually i cannot dial out from any of client.
sip.conf has [110] client with context=from-internal, and i added exten=>_9989XXXXXXXX,1,Dial(SIP//${EXTEN}$sip-in)