Telephone numbers
New geographic, non-geographic or direct-dial numbers where available and suitable.
SIP and VoIP trunks
Connect your phone system to the numbers customers call.
39T provides managed SIP and VoIP trunk services for compatible business phone systems, including UK telephone numbers, DDIs, porting, call capacity and continuity options.
Managed telephone serviceNumbers, channels and routing
- New UK numbers and DDIs where available
- Eligible number porting and migration support
- Inbound and outbound call capacity
- Fraud controls and continuity options
What the service can include
More than a username and password.
A business trunk should be sized, secured and tested around the phone system and the organisation’s calling patterns.
Call channels
Capacity for the expected number of simultaneous inbound and outbound calls.
Number porting
Coordinate eligible number transfers using accurate account details and agreed migration dates.
Fraud controls
Apply appropriate international restrictions, authentication, alerting and account controls.
Inbound routing
Route numbers to the correct system, site, queue or agreed failover destination.
Fault ownership
Give the business a clear route for investigating trunk, number and call-routing faults.
From caller to colleague
Every stage needs to be configured and tested.
Public number→SIP / VoIP trunk→3CX users
Number porting
Do not cancel the old service before the port completes.
Porting depends on exact matching records and the current provider’s process. Cancelling an existing service too early can put numbers at risk.
- Collect bills and account information
- Identify single numbers, ranges and dependent services
- Agree the target date and call-routing plan
- Test inbound, outbound and presentation after porting
Security and compliance
Control who can place calls and where.
SIP credentials, administrative access, international destinations and unusual call patterns should be managed carefully. Emergency-service address information must also be kept accurate for services that support emergency calling.
Review existing trunks
We can review current numbers, channels, renewal dates, call spend, fraud controls and compatibility with a proposed 3CX system.
Request a trunk reviewComplete business voice
Connect the trunk to a managed system.
SIP trunk FAQs
Numbers, channels and migration.
What is a SIP trunk?
A SIP trunk connects a compatible business phone system to public telephone networks over IP. It can carry inbound and outbound calls and associated telephone numbers.
Can we keep our existing numbers?
Many UK geographic and non-geographic numbers can be ported, but eligibility depends on the number type, current provider, account information and accepted porting documentation.
How many call channels do we need?
The required capacity depends on peak simultaneous calls, queues, outbound activity, conference use and growth. 39T sizes the service around actual call patterns rather than only the number of users.
Can calls fail over if our phone system is unavailable?
Depending on the carrier and service design, inbound calls may be diverted to alternative numbers or destinations. This should be agreed and tested as part of the continuity plan.