Multi-line VoIP phone systems

What multi-line means on VoIP

With traditional lines, "multi-line" meant exactly that: one copper line per call, several lines grouped behind a main number, and a phone system with a button for each line. Adding capacity meant ordering another line.

A VoIP phone system separates the three things a line used to do:

• Capacity: how many calls can run at once, set by licences, SIP channels or simultaneous calls and by the bandwidth of your connection
• Numbers: as many main, department and direct-dial numbers as you need, none of them tied to a physical line
• Answering: which phones, apps and people each call reaches, set by groups, queues and menus

So a growing business adds users and numbers as settings, and checks capacity, rather than ordering new lines. If you are moving off several lines or ISDN today, ISDN to VoIP and switching from landline to VoIP cover the move.

How many calls at once: capacity by platform

Each platform sets call capacity in its own way. This is how the platforms Forever Systems supplies handle it:

Whatever the licensing, every call also uses bandwidth. Cisco's figures, including network overhead, are about 87.2 kbps in each direction per call with G.711 or G.722 and about 31.2 kbps with G.729, so multiply by your busiest moment and check the connection with our VoIP requirements checklist. Our sister site explains how many SIP channels you need from your call logs.

Numbers: main lines, departments and direct dials

A multi-line VoIP phone system can hold as many numbers as you need. A common plan is a main number into a menu or reception, department numbers for sales, accounts and support, and a direct dial (DDI) for each person who takes calls from regular contacts. Local 01 and 02 numbers give each office a local presence, and an 03 number gives a single national one.

Existing numbers, including ISDN DDI ranges, can usually be ported across. VoIP numbers for business explains the number types, and port your landline number to VoIP covers the move.

Line keys, BLF and shared lines on desk phones

On a desk phone, "lines" become programmable keys. The ones that make a multi-line system work for busy teams are:

• Line keys for each number or call appearance, so a user can hold one call and take another
• BLF (busy lamp field) keys that light up to show whether a colleague is free, ringing or on a call, and pick up or transfer with one press
• Shared lines that let several phones answer and pick up the same number, such as a department line
• Call park keys so a call can be parked and picked up from any phone
• Expansion modules that add rows of BLF keys for a receptionist covering many people

Key counts and screen sizes vary by handset, which is why reception and executive phones sit in a higher tier; VoIP desk phones for business explains the tiers. VoIP desk, cordless and conference handsets can be bought outright or, in some cases, included in your monthly rental, with the options confirmed at quote. Softphone apps show presence and transfers on screen instead of keys.

Hunt groups, queues and auto attendants

Sharing calls across a team is where a multi-line VoIP phone system earns its keep:

• Hunt groups (ring groups) ring several people at once, in order or in rotation, so the first free person answers
• Call queues hold callers in turn with music or messages until an agent is free, instead of a busy tone
• Auto attendants greet callers with a menu and route them by department, opening hours or holidays

Platform tiers differ. On 3CX, call queues are included in SMB Free, PRO and AI, but not in Basic. Forever UC includes a call queue in its Standard tier, and Contact adds live contact centre reports. Teams Phone provides auto attendants and call queues, each using a resource account. Webex Calling provides hunt groups and call queues, and Cisco's Webex Calling Customer Assist add-on upgrades the queues with agent and supervisor tools. If calls need recording or reporting, see VoIP call recording and VoIP phone system features.

Several sites on one system

A multi-line VoIP phone system does not stop at one building. Put every office on one system and staff share one extension range and dial plan, calls between sites are internal transfers, and each site keeps its own local numbers, menus and opening hours. Head office can manage every site from one portal.

Each platform organises sites its own way: 3CX includes multi-site support in its PRO and AI editions; Teams Phone runs the whole organisation in one tenant with PSTN options that can be mixed by user or site; Webex Calling is organised by locations in Control Hub, each with its own numbers and PSTN connection; and Forever UC connects every site and home worker to the same hosted platform.

Each site's connection becomes important, so plan for capacity and a backup path where calls are business-critical; our sister site covers the leased line for VoIP option. For the full multi-site picture, including emergency addresses and resilience, see the guide to choosing a multi-site phone system.

How we help

Forever Systems supplies 3CX, Microsoft Teams Phone, Webex Calling, Forever UC, Forever Teams and SIP trunks, so we can size and design a multi-line system around how your calls actually arrive. We can help with:

• Capacity planning from your call logs, covering licences, channels and bandwidth
• A number plan of main, department and direct-dial numbers, with your existing numbers ported
• Hunt groups, queues and menus for each team and site
• Desk phones with the right key layout for reception and team leaders, plus apps for everyone else

Contact us with your number of users, sites and lines today, and we will recommend a set-up.