How do I configure smartphones that has 3CX app so it can be used in LAN and outside the office?
It works locally, but once outside the office, how does it know to connect to my office 3cx phone system?
You need no special configuration for your 3CX client to work inside or outside your network. The welcome email for 3CX Clients, contains all necessary settings for your application to work. Furthermore, your client when outside your network, uses the 3CX Tunnel in order to connect to your PBX. The configuration settings can been seen in your 3CX client under Settings>>Accounts(select your account)>>SERVER SETTINGS. You can find detailed "how to" information here. For any questions you might come up with, please do feel free to contact.