Phone systems are boring right up until they are not. For a professional office the choice matters more than most people expect, because the phone is often the first contact a client has and because in regulated practices the call itself may be a compliance question.
The things that actually matter
Call quality depends on your internet, not the provider. Most VoIP complaints are network problems. Before choosing anything, find out whether your connection can prioritise voice traffic and whether your upload speed is adequate. A cheap system on a good connection beats an expensive one on a poor connection every time.
What happens when the internet fails. Monsoon season is a real consideration in Arizona. Ask specifically how calls route when your office connection drops. Automatic failover to mobiles is standard and worth confirming rather than assuming.
Number portability. Confirm in writing that you can take your numbers with you. Practices have been held hostage by this.
Does it integrate with what you use. Practice management, CRM, EHR. Screen pops and click to dial are small conveniences that compound across a day.
The compliance questions nobody asks
For medical practices. If voicemail contains patient information, or if the system stores or transcribes calls, the vendor is handling protected health information and needs a business associate agreement. Many practices sign up for a phone system without ever considering this.
For CPA firms. If client financial information passes through voicemail or recordings, the vendor falls under your service provider obligations. Same principle.
Call recording. Arizona is a one party consent state for recording, but that is the criminal law position and it is not the whole picture for a business. Sector rules and your own professional obligations may impose more. If you plan to record, get advice specific to your profession rather than relying on the general rule.
Where do recordings live, and for how long. Storage location, retention period, encryption and who at the vendor can access them.
The practical advice
Do not choose on price per seat. The differences are small and the switching costs are not.
Ask for a trial with two or three real users on your real network before committing. Everything sounds fine in a demo.
And check the contract for what happens at the end, particularly around numbers and data, because that is where the friction always is.