Analogue vs SIP vs VoIP: What's the Difference?
Analogue is the traditional copper-wire phone technology being phased out ahead of the PSTN switch-off. VoIP is the broad umbrella term for making calls over the internet instead of a physical phone line. SIP is the specific technical protocol that most VoIP systems — including SIP trunks connecting to an on-premise PBX — actually use to set up and manage those calls. They're not three competing options so much as three different layers of the same story: analogue is what's being replaced, VoIP is the general replacement, and SIP is the technology doing much of the work underneath it.
What Is Analogue?
Analogue phone lines are the traditional copper-wire technology that's carried phone calls in the UK for well over a century. Each line typically supports a single call at a time, and the phone itself drew a small amount of power directly from the line — which is why an old corded phone would often keep working during a power cut. Analogue lines are being permanently withdrawn as part of the PSTN switch-off, with a final national deadline of 31 January 2027.
What Is VoIP?
VoIP stands for Voice over Internet Protocol — calls carried as data over an internet connection rather than a dedicated phone line. It's a broad umbrella term covering everything from a simple softphone app on a laptop through to a fully hosted business phone system like Gamma Horizon. When people say "VoIP phone system," they're usually referring to hosted VoIP specifically, where the entire phone system runs in the cloud rather than on-site.
What Is SIP?
SIP stands for Session Initiation Protocol, the specific technical standard used to establish, manage, and end a voice call over the internet. It's not a phone system in its own right — it's the underlying mechanism many VoIP services use to make calling actually work. The clearest everyday example is a SIP trunk, which uses this protocol to connect an existing on-premise PBX system, such as 3CX, to the wider telephone network. Our guide to what a SIP trunk is covers this specific use in more detail.
How Do They Relate to Each Other?
Think of it as layers rather than a straight comparison:
- Analogue is the older technology being retired
- VoIP is the general category of internet-based calling that's replacing it
- SIP is one of the key technical protocols that makes VoIP calling work, particularly relevant when connecting your own phone system rather than using a fully hosted one
In practice, most VoIP services use SIP somewhere under the hood, even if the term never comes up when you're using a hosted system day to day. It only becomes a term you need to know directly if you're connecting your own on-premise PBX, rather than using a fully managed platform.
Comparing the Options for Your Business
| Analogue | SIP Trunking | Hosted VoIP | |
|---|---|---|---|
| Infrastructure | Physical copper line | Internet connection + your own PBX | Internet connection only, fully cloud-based |
| Availability | Being withdrawn nationally by 31 Jan 2027 | Available now | Available now |
| Scalability | Limited, physical lines needed | Flexible, channels added on demand | Highly flexible, users added instantly |
| Management | Provider-managed hardware | You manage the PBX; provider manages the trunk | Fully managed by the provider |
| Best suited to | No longer a viable long-term option | Businesses with an existing PBX investment | Businesses wanting a simple, fully managed system |
Which Should Your Business Choose?
Analogue isn't a genuine long-term option any more, given the switch-off timeline — our 90-day switch-off checklist is worth reading if you're still migrating. Between SIP trunking and hosted VoIP, the choice usually comes down to whether you already have, or specifically want, your own on-premise phone system. If you do, SIP trunking connects it to the outside world. If you'd rather not manage phone system hardware or software at all, a hosted VoIP platform handles everything as a single service.
Frequently Asked Questions
Is VoIP the same thing as SIP? No. VoIP is the general category of internet-based calling. SIP is one of the specific protocols commonly used to make VoIP calls work, particularly in SIP trunking setups.
Can I still use analogue equipment with a VoIP or SIP system? Some analogue devices, such as older fax machines or alarm systems, can be connected via an analogue telephone adapter (ATA), but this isn't the same as running the device on a genuine analogue line, and not every device is compatible.
Is hosted VoIP more reliable than SIP trunking? Reliability depends more on your specific setup and internet connection than the category itself — both can be highly reliable when configured correctly, and both depend entirely on a working internet connection, unlike old analogue lines.
Do I need to understand SIP to switch to VoIP? Not if you're moving to a fully hosted system like Gamma Horizon, where this is handled entirely by the provider. It becomes more relevant if you're keeping your own PBX system and connecting it via SIP trunking.
Untangling the terminology is the easy part — choosing the right setup for how your business actually works is the bit worth getting right. Request a quote for independent advice, or use our phone system finder to compare your options.
