"One bill" is the most over-promised phrase in B2B telecoms. Most consolidated invoices we see are still two PDFs and a separate mobile portal with a different login. That is not consolidation, that is bundling.
A genuine one-bill setup means a single monthly invoice that lists every charge — lines, calls, SIP, mobile, broadband, hosting, SaaS licensing and managed services — with itemised per-SIM and per-extension breakdown, in a format your finance team can import.
It also means a single account manager who can answer questions about any line on that invoice without escalating into three different teams.
When you ask a supplier for "one bill," ask them to show you a sample invoice. If they cannot, you are buying a bundle, not a consolidation.