We have a growing team of volunteers that are making calls on behalf of the church. They are using their own cell phones for this and understandably they want the call to come from the church’s number rather than from their personal cell phone.
We have an older VoIP phone system; it’s been fine so we don’t have any plans to upgrade it. Our phone service provider offered an app (Vodia) to do this but it’s not reliable - seems to only work with some phone models. So, we are exploring options.
One suggested Open Phone. Looks like you have to port your number to them, so it’s unclear how that would affect existing service.
Without porting your number, or somehow putting another system between your current phone system and your lines - you have limited options.
What I have seen people do in the past is use http://grasshopper.com for this application, on it’s own number. So volunteers can call out and all appear as coming from that unique number. You can then setup a call forwarding rule in grasshopper for inbound calls to forward to your main line.
You can still set caller ID and such on the grasshopper line to match the churches - so other than the numbers being different, it otherwise all works how you might want.
If it absolutely must be a single number - and you don’t want to replace your old phone system - then you’ll want to add a new call processor in front of your old phone system, and establish trunking/dialing plan rules to move calls around. 3CX is often used for this, but tons of options. A bit more technically advanced - and more moving parts to buy and maintain - but it would allow a singular number.
3CX is simple and affordable. You can run it from a VM, Raspberry Pi, or your cloud. They have a smartphone app. We run it as our main PBX and it is by far the least expensive way to go.