Match the delivery method to your system
Sellers deliver VoIP numbers in one of three ways: registration credentials your PBX signs into, IP authentication where the carrier trusts your address, or a trunk you terminate. Each one implies different firewall and NAT work on your side. The offer states which you get, and the order chat is where you exchange the IP or domain — never a private messenger.
- Registration suits a single PBX behind NAT
- IP authentication suits a static, always-on softswitch
- Confirm codec support (G.711, G.729, Opus) before you fund
Channels decide capacity, not price
A cheap DID with one channel drops your second simultaneous caller. Work out peak concurrency first, then filter the board by channels and read what the seller says about bursting. If you expect campaign traffic, say so in the order chat so the seller can confirm the range tolerates it.
Native versus ported ranges
Native ranges sit directly on the seller's carrier; ported ranges were moved in from another operator and depend on that history staying clean. Ported blocks are often cheaper and are perfectly usable, but they carry more risk of being reclaimed during a carrier audit. Where continuity matters, prefer native ranges with a replacement guarantee.
- Native: fewer moving parts, usually survives audits better
- Ported: cheaper, worth pairing with a longer replacement window
- Ask when the range was last audited by the upstream
Pricing structures you will meet
Wholesale VoIP numbers usually combine a one-off setup fee with a monthly price per number, and sometimes a per-minute inbound charge on top. Toll-free ranges nearly always add per-minute inbound. Every DIDDock offer states setup fee, billing unit and minimum order so a per-number price cannot hide a large activation cost.
Testing before the money moves
Once escrow is funded and the seller assigns the range, register your endpoint and place inbound tests from at least two networks, including a mobile one. Check CLI presentation, audio in both directions and how quickly calls set up. Anything wrong goes into the order page as a dispute while the funds are still held.