SIP Trunks in Amersham
SIP trunking for businesses with an existing PBX - replace ISDN lines with cost-effective, flexible SIP channels managed by Crushed Ice. Serving businesses in Amersham and surrounding areas.
SIP Trunks in Amersham
SIP (Session Initiation Protocol) trunks replace traditional ISDN and PSTN telephone lines by carrying calls over your internet connection. With the Openreach ISDN switch-off now complete, any business still running an on-premise PBX needs SIP trunks to maintain PSTN connectivity. Crushed Ice supplies and manages SIP trunks with right-sized concurrent call capacity, competitive per-minute call rates, full number porting for all your existing DDIs and main numbers, and configurable failover routing. If you want to keep your existing phone system hardware but need to replace your ISDN lines, SIP trunks are the answer. Worth noting: our full hosted phone system offering includes one SIP trunk per user as standard, so there is no need to think about concurrent channel provisioning at all. For businesses considering a full system replacement rather than just ISDN migration, our hosted PBX is worth a conversation.
Crushed Ice provides sip trunks to businesses throughout Amersham - remote configuration and on-site deployment handled as standard.
What's covered
PBX Compatibility
SIP trunks work with virtually all on-premise PBX systems: Avaya, Mitel, Panasonic, Cisco, Asterisk, 3CX. We test compatibility before provisioning.
Number Porting
Port your existing geographic numbers, DDIs, 0800, 0845, and 03 numbers to SIP. No changes to your public-facing numbers.
Elastic Channels
Concurrent call channels scaled to match your actual usage. Add capacity in hours, not weeks. No over-provisioning required.
HD Voice Quality
G.722 wideband audio delivers noticeably clearer call quality than traditional ISDN, provided you have a suitable internet connection.
Lower Call Costs
Competitive UK, European, and international per-minute rates. Most businesses save 20–40% on their call costs compared to ISDN equivalents.
Failover Routing
We can configure incoming call diversion so that if your internet connection fails, calls are redirected to mobile numbers or a backup destination rather than simply ringing out. This is available as a configurable option on all SIP trunk deployments.
How it works in practice
Emergency ISDN Replacement
The situation
A legal firm's telecoms provider gave 30 days notice that their ISDN30 circuit was being withdrawn. They had an on-premise Panasonic PBX they were not ready to replace.
The result
Crushed Ice provisioned SIP trunks compatible with their Panasonic system within a week, ported their 25 DDIs, and cancelled their ISDN contract, saving £340 per month in line rental.
Multi-Site Single Bill
The situation
A property company had three offices each with separate ISDN lines, separate telecoms providers, and three separate monthly invoices. Call transfers between sites went via the PSTN, incurring per-minute charges.
The result
SIP trunks from a single provider, centrally managed by Crushed Ice, replaced all three sites' ISDN lines. Internal site-to-site calls became free, and three bills became one. A 35% overall cost reduction.
Burst Capacity for Seasonal Demand
The situation
A retail business with a customer services team needed additional call capacity during peak periods (November–January) but was paying for excess ISDN channels year-round.
The result
SIP trunks with elastic capacity allowed them to scale from 10 to 25 concurrent channels for peak season and back to 10 in January, paying only for what they actually used.
Significant Cost Reduction Without Changing the PBX
The situation
A distribution company was happy with their existing Mitel PBX but their ISDN bills had become excessive, over £800 per month for line rental and calls.
The result
Crushed Ice replaced their ISDN lines with SIP trunks, keeping the Mitel system unchanged. Monthly telecom spend dropped from £820 to £380, a 54% reduction, with improved call quality.
Porting your numbers
Capacity Planning
We analyse your current call volumes and concurrent call patterns to determine how many SIP channels you actually need. Most businesses are over-provisioned on ISDN. SIP lets you right-size immediately.
PBX Configuration
We configure the SIP trunk registration on your existing PBX: codec settings, registration credentials, dialplan adjustments, and failover rules. This is done remotely and typically takes two to four hours.
Number Porting
We initiate porting of your existing numbers from your current ISDN provider. Numbers are ported with your PBX handling both old ISDN and new SIP trunks in parallel during the transition, with no downtime.
Testing & Go Live
We perform end-to-end call testing: inbound, outbound, DDI routing, voicemail, and failover, before confirming go live. Ongoing management is included in your monthly agreement.
Delivered as part of our Business VoIP Phone Systems service
SIP Trunks are a core part of how Crushed Ice delivers Business VoIP Phone Systems. All of our services run on a simple all-inclusive monthly fee - no large upfront costs, no hidden extras, and direct access to the people who actually look after your systems.
SIP trunks - common questions
Providing SIP Trunks to businesses across HP6, HP7 in Amersham
