The short version. Compare the same workload on the same billing term. Keep unknown costs visible until the provider answers them.
Write down the job before the price
Use one month of expected work: number of staff, business lines, new conversations, replies and attachments. Add calling only if your team needs it. The same number of messages can represent a few long conversations or many first contacts; providers may price and limit those differently.
Make a worksheet with quantity, unit, rate, billing period and source columns. A quote for inbound replies belongs on a different row from permission to initiate a conversation.
Separate launch cash from recurring cost
First-month cash equals setup, required equipment, implementation work and the first recurring bill. A twelve-month estimate adds eleven more recurring bills and expected usage. Keep annual prepayment in the cash column even when a provider advertises a monthly equivalent.
For illustration only, a hypothetical $100 line with $200 setup costs $300 to launch and $1,400 for twelve months before usage or staff time. A second line might repeat setup; ask instead of multiplying an assumed discount.
Leave a place for the unanswered questions
Mark unknown allowances as awaiting confirmation rather than zero. Include fallback charges, number rental, extra seats, overages and the cost of exporting data or running old and new tools together during a move.
Bring the completed sheet to each provider and request a written total for that workload. Retain the dated quote and the plan name. A precise comparison is more useful than a cheapest-first ranking built from incompatible headlines.
Sources & further reading
These provider pages were checked for this edition. Provider statements are not independent verification of performance.