Singapore business phone planning

SIP trunk or existing telephone lines: what changes?

A SIP trunk provides a connection between a compatible telephone system, such as an IP PBX or VoIP phone system, and the public telephone network over an IP connection. The telephone system and the carrier connection perform different jobs. Buying a PBX subscription does not, by itself, establish the external calling service your business needs. StarHub SmartSIP.

Compare the actual service, not just the label

Scroll the table sideways on small screens.

Questions to compare the proposals
Decision	Questions for an existing line service	Questions for a SIP proposal
Capacity	How many calls can the current arrangement handle?	What external call capacity is included, and how is it counted?
Equipment	Which PBX and special-purpose devices depend on it?	Which PBX, gateways and devices are supported?
Connectivity	What connections and power arrangements are needed today?	What connectivity does the carrier require, and who manages it?
Numbers	Who owns the service account and manages changes?	Is each number eligible for the proposed migration?
Costs	What rental, usage, maintenance and exit costs apply?	What setup, recurring and usage charges are excluded from the proposal?

Do not assume every SIP service uses the same connectivity model. Ask the carrier to document the design and responsibilities. Singtel describes its SIP offer as a specific business service; that description is not evidence that another provider supplies an identical arrangement. Singtel SIP.

A useful next step

Bring the current service inventory, number list, contract dates and busy-period call requirements to the assessment. Include fax, alarms or other equipment that depends on existing lines. Agree acceptance tests and a fallback plan before cancelling anything. Compare the complete quotation after compatibility and eligibility have been confirmed.

How a SIP trunk fits with a cloud PBX

A cloud PBX such as LinkusPBX holds your extensions, menus and queues. A SIP trunk is the carrier service that connects it to ordinary phone numbers. You need both for external calling. The PBX price and the trunk price are separate, and the trunk is quoted per customer according to numbers, channels and call usage.

Checklist: information to gather before comparing

Every number you use today, including fax and alarm lines, with the carrier for each.
Your current contract end dates and any early termination terms.
Peak simultaneous external calls, from bills, PABX reports or a best estimate.
Whether you need outbound caller ID to show a particular number.
Equipment that depends on analog lines: card terminals, lift phones, alarm panels, fax.
Your internet service and whether a backup connection is available.

A typical switch-over sequence

Assess numbers and equipment, and confirm porting eligibility with the carrier.
Set up the PBX and SIP trunk, and test with a temporary number where possible.
Move special-purpose lines (alarms, lifts, fax) to a suitable gateway or keep them on existing lines.
Port the main numbers on an agreed date.
Test inbound and outbound calls from several networks.
Only then cancel old services that are no longer needed.

Common mistakes

Cancelling old lines too early and losing a number.
Forgetting a lift or alarm line that still needs an analog connection.
Comparing a PBX-only price against a bundled telco quote.
Not checking SIP ALG and QoS settings on the office router; see the network readiness checklist.

Number porting and setup are quoted case by case. See keeping your business number.

Questions to ask a SIP trunk provider

How many simultaneous calls are included, and how are extra channels charged?
How are local, mobile and international calls billed?
Can existing numbers be ported, and is the whole number block required?
What caller ID options are allowed?
What support hours and escalation contacts apply?

Frequently asked questions

Do I need a SIP trunk with a cloud PBX?

For calls to and from ordinary phone numbers, yes. The PBX and the SIP trunk are separate services and are quoted separately.

Can I keep my existing numbers on a SIP trunk?

Often, depending on the current carrier, line type and contract. Eligibility is checked first, and porting is quoted case by case.

What happens to my fax or alarm line?

It may need an analog gateway or may need to stay on an existing line. We check each one during assessment.