At 900 leads a month with three callers, the $22,000 is mostly buying two things: someone deciding what your data model is before it gets built, and reporting that survives contact with how your team actually types. Template builds work when your process matches the template. Yours has three lead sources with different economics and a dispo pipeline, which means attribution has to hold from campaign through contract, and that's where templates break, because they usually stamp a single source field on the record and lose it the moment the lead gets re-engaged from a different channel.
Pike's point on the 40k records is the right first question, and I'd extend it. Ask both quotes what they do with a duplicate: merge, keep the newest, keep the one with call history? At your volume the dedupe rule determines your entire callback report, and if it's wrong you'll spend months looking at conversion numbers that are off by the duplicate rate.
The failure mode to fear with A isn't a broken build. It's a build that works and that your callers route around. If disposition codes take four clicks, the phones will pick whatever code is fastest and your reporting turns into fiction inside six weeks. Ask A directly who trains the team and what happens in week five when the codes aren't being used.
The failure mode with B is the $2,500 a month. Get the retainer defined as deliverables rather than access, because "ongoing support" at that price on a system that isn't changing is a subscription to nothing. And ask B what the discovery phase produces as a document you own. If the answer is a slide deck, that's most of the gap between the quotes right there.
One structural thing: whoever you pick, the platform account, phone numbers, and API keys go in your name. Recovering registered sending numbers from a departed vendor is slow.
