I can use Ext to call other people now, but I don't need to call outside. For example, mobile phone. Do I have to set the VOIP or SIP Trunks to get an outside line? . Thank you very much!
Did you mean to say " I do need to call outside..."? If that is the case, then, yes, you will need a VoIP trunk, or a PSTN/ISDN gateway if you wish to make "outside" calls. If you do have a trunk, then you will need to create outbound rules. https://www.3cx.com/blog/voip-howto/outbound-rules-a-complete-example/
When it comes to it I would recommend you use supported SIP trunks or Gateways: SIP Trunks: https://www.3cx.com/partners/sip-trunks/ Gateways: https://www.3cx.com/voip-gateways/
You need at least one outbound rule and at least one sip trunk. I use flowroute for a cheap supported trunk.
