ai-receptionist.com sells extra minutes as prepaid booster packs at one rate across its whole ladder, and states that the packs never expire. Its country gate is explicit, from its own FAQ: "Currently, we provide phone numbers and service in the United States and Canada."
Its ladder is unusual in that the first two plans include the same number of minutes, so that step buys AI quality and extra transfer contacts rather than capacity. And because one booster rate applies to every plan, the entry plan plus packs undercuts the plans above it at any volume, which is the vendor's own arithmetic rather than a quirk of ours.