The portability point is critical and not talked about enough. Great framework here.
One thing worth layering on top of this setup: whatever number becomes your primary customer-facing line, what happens to calls that come in after hours or when everyone is tied up? RingCentral handles transcription great, but the call still goes to voicemail.
The businesses I've seen scale past the owner as bottleneck problem fastest are the ones who solved the inbound capture piece. Not just who owns the number, but what actually happens to every call that comes in. That is where a lot of jobs quietly walk out the door.
