By the Maincoms engineering team, Cosham, Portsmouth. Updated 17 October 2026.
In short: A hosted (cloud) phone system suits most small and medium businesses, particularly those with home or mobile workers. An on-site system suits larger sites, specialist equipment and organisations that want to own their system. A hybrid setup extends an existing on-site system to remote staff.
With ISDN and analogue lines closing, many businesses are replacing a phone system that has worked quietly for years. The choice usually comes down to where the system lives.
Hosted (cloud) systems
With a hosted system, the phone system runs in a data centre and your phones connect to it over the internet. Platforms such as Gamma Horizon and Yeastar P-Series Cloud Edition work this way.
- Low upfront cost. You pay a monthly charge per user rather than buying a system outright.
- Works anywhere. Staff can take calls on a desk phone, a laptop or a mobile app, in the office or at home.
- Easy to change. Adding a user or changing call routing is quick and does not need hardware.
It suits most small and medium businesses, especially those with home or mobile workers.
On-site systems
An on-site system is a small appliance in your building, such as a Yeastar P-Series PBX, connected to SIP trunks for outside calls.
- Lower running costs over time for larger numbers of users, because there is no per-user hosting fee.
- Local control. Internal calls and features keep working even if the internet connection drops.
- Integration with existing equipment, such as door entry, paging or older analogue handsets in a warehouse.
It suits larger sites, businesses with specialist equipment, and organisations that prefer to own their system.
Hybrid
A hybrid approach keeps an on-site system for the main building while giving remote staff the same features through mobile and desktop apps. It is often the right answer for businesses that have invested in a system and want to extend it rather than replace it.
Questions to answer before you choose
- How many people need a phone, and how many work away from the office?
- Do you have a call queue, reception or contact centre that needs reporting?
- What else connects to your phone lines today, such as door entry or alarms?
- How good is your internet connection, and do you have a backup?
Whichever you choose, call quality depends on your network. Most problems we are asked to fix trace back to the local network rather than the phone system, which is why we check bandwidth and network settings before installing anything.
See business phone systems or ask an engineer which option suits you.
Frequently asked questions
Can we keep our existing phone numbers?
Yes. Numbers are ported to the new system, so callers dial the same numbers as before.
What happens to a hosted phone system if the internet goes down?
Calls can divert automatically to mobiles or another site, and a 4G or 5G backup connection keeps the phones running while the main line is repaired.
Can staff use a mobile as their office extension?
Yes. Hosted systems such as Gamma Horizon and Yeastar include mobile and desktop apps, so staff can make and take calls from their office number wherever they are.
Will our ISDN phone system still work after 2027?
Not on ISDN, as the service is being withdrawn. Some on-site systems can be moved onto SIP trunks and kept, while others are better replaced. An engineer can check yours.