[jozef]

When you log in to PBXes you see:

Welcome
People Can reach your PBX by calling LoginID@pbxes.org

SIP URIs can also be:
LoginID@sip.pbxes.org
LoginID@pbxes.com
LoginID@sip.pbxes.com

If you have only one Extension for incoming calls, you will only need one blank Incoming Route pointed to your Extension.

It does not matter what you type in the SIP URI after LoginID or from which provider coming call in, everything is pointed to your Extension by the blank Incoming Route.

With several extension number you need more Incoming Route's:

    SIP URI          ; Incoming Route; Extension
LoginID@pbxes.org    ;               ;     200
LoginID-200@pbxes.org; LoginID-200   ;     200
LoginID-201@pbxes.org; LoginID-201   ;     201
LoginID-202@pbxes.org; LoginID-202   ;     202

If someone calls the SIP URI LoginID-900@pbxes.org call is connected to extention 200 by blank Incoming Route.