Open the "SIP Trunks" tab
Open the Voxtelesys SIP Trunk
Change your Main Trunk Number to have the +1 in front.
If you have a rule for your main number under Inbound rules you will need to delete the rule first.
If you have more DIDs to add click on the "DIDs" tab at the top.
Add a +1 in front of your other DIDs.
Click "OK" to save changes.
Update your Outbound rules following our guide if you do not want to dial +1 when calling out.
You could also read our written tutorial here.