Cisco CUCM
Cisco Unified Communications Manager (CUCM) runs many larger UK offices. The most common fault we see searched for is a phone that won't register, and the most common task is finding the right handset guide.
The 7900 series has been out of support since June 2023. Plan to replace those phones, and don't buy them second-hand. Cisco's current desk phones are the 9800 series (9811, 9841, 9851, 9861 and 9871). The 7800 series is being withdrawn too: the last order date for the 7821 was 28 October 2026 ↗. Check Cisco's notices ↗ for your model.
For the network side of registration faults, read Voice VLANs and DHCP for desk phones.
Most Cisco phone problems in offices fall into two groups: phones that won't start or register, and people who need the right guide for their model. The registration guide follows the phone's start-up step by step, so the last message on screen tells you where it stopped. The phone-guides page helps you read the model label and choose the right official document.
Both link to our plain-English explainer on voice VLANs and DHCP, which covers the network side of many start-up faults.
How a call travels through Cisco CUCM
Press a stage, or let it play. Each one shows what to look at without changing anything.
One phone or all of them?
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Free infographics for this topic
One-page summaries of each guide, free to print, pin or share with credit. Click one to open its guide, where you can download the PNG.
