Glossary / Billing, Numbering and Telecom Business
💰 Billing, Numbering and Telecom Business covers the commercial, regulatory, and numbering terms you encounter when choosing and managing a business phone service. This section contains 21 terms, from pricing models and SLAs to international numbering standards and wholesale voice markets.
On this page: SLA · Uptime/Availability · Per-User Pricing · Per-Channel Pricing · Bundled Minutes/Unlimited Calling · Per-Minute Billing · Number Rental · Porting Fee · Interconnection · ITSP · LNP · ENUM · E.164 · CLI · P-Asserted-Identity · Least Cost Routing · A-Number/B-Number · Origination/Termination · Wholesale Voice · SMS Aggregator · TCO
SLA (Service Level Agreement)
A contract between you and your Cloud PBX provider that guarantees a minimum level of service quality. The most common SLA metric is uptime (e.g., 99.9% availability per year). The SLA also defines what happens when the provider fails to meet the guarantee, typically a credit on your next bill. Always read the SLA before signing, and check how the provider measures downtime.
Related: Uptime/Availability · TCO
Uptime / Availability
The percentage of time the phone service is operational and accessible. An uptime of 99.9% means the system may be down for a maximum of about 8.7 hours per year. 99.99% means less than 53 minutes of downtime per year. Higher uptime usually means the provider has redundant infrastructure across multiple data centres. This is one of the most important factors when comparing providers.
Related: SLA · Failover
Per-User Pricing
A billing model where you pay a fixed monthly fee for each user (employee) who has a phone account. This is the most common pricing model for Cloud PBX services. It is simple to budget because costs scale directly with team size. Some providers include calling minutes in the per-user fee; others charge calls separately. Compare what is included before choosing.
Related: Per-Channel Pricing · Bundled Minutes/Unlimited Calling · TCO
Per-Channel Pricing
A billing model where you pay based on the number of simultaneous calls (channels) your system can handle, rather than the number of users. This is more common with SIP trunking services than with hosted Cloud PBX. It works well for businesses where many employees share a few phone lines (e.g., a warehouse with 50 staff but only 5 phones).
Related: Per-User Pricing · Concurrent Call
Bundled Minutes / Unlimited Calling
A pricing plan that includes a set number of calling minutes (or unlimited calls) within the monthly fee. Bundled plans typically cover domestic calls and sometimes calls to neighbouring countries. Calls beyond the bundle or to excluded destinations are charged per minute. "Unlimited" plans usually have a fair-use policy that limits extremely high usage.
Related: Per-Minute Billing · Per-User Pricing
Per-Minute Billing
A pricing model where every call is charged based on its duration. Rates differ by destination (local, national, mobile, international). This model is common for SIP trunking or pay-as-you-go plans. It can be cheaper for businesses with low call volumes, but costs become unpredictable for high-volume callers. Always check the per-minute rates to the countries you call most.
Related: Bundled Minutes/Unlimited Calling · Least Cost Routing
Number Rental
The monthly fee your provider charges for each phone number (DID) assigned to your account. You typically pay a small fee per number per month, whether or not you use it. If your business needs many numbers (e.g., one per employee, or numbers in different cities), the rental costs add up. Some providers include one or more numbers in the base plan.
Related: DID / DDI · Porting Fee
Porting Fee
A one-time charge applied when you transfer (port) your existing phone numbers from one provider to another. Not all providers charge a porting fee; some waive it to attract new customers. The fee covers the administrative work of coordinating the number transfer between the old and new carrier. Porting itself is a legal right in the EU.
Related: LNP · Number Rental · Number Porting
Interconnection
The physical and commercial arrangement that allows calls to flow between different telecom networks. When you call someone on a different provider, the call crosses an interconnection point. Providers negotiate interconnection agreements and charge each other for terminating calls. These costs are part of what determines your per-minute call rates.
Related: Origination/Termination · Wholesale Voice
ITSP (Internet Telephony Service Provider)
A company that provides voice services over the internet using SIP. An ITSP supplies SIP trunks, phone numbers, and connectivity to the public phone network. Your Cloud PBX provider is typically also an ITSP, or works with one behind the scenes. When comparing providers, you are essentially comparing ITSPs and their coverage, pricing, and quality.
Related: SIP Trunk · Interconnection
LNP (Local Number Portability)
The regulation that allows businesses and individuals to keep their phone numbers when switching providers. LNP is a legal requirement in the EU and most developed countries. The process involves your new provider submitting a porting request to your current provider. The timeline varies by country, from a few days to several weeks.
Related: Porting Fee · E.164 · Number Porting
ENUM (E.164 Number Mapping)
A system that maps traditional phone numbers (E.164 format) to internet addresses (SIP URIs) using DNS. When a provider looks up a phone number in the ENUM database and finds a SIP address, it can route the call directly over the internet, bypassing the traditional phone network. This can reduce costs and improve quality. ENUM adoption varies by country.
Related: E.164 · SIP URI
E.164
The international standard for formatting phone numbers. An E.164 number starts with a country code, followed by the national number, with no spaces, dashes, or brackets. For example, a Luxembourg landline: +35226340100. SIP systems use E.164 format internally to route calls correctly across international borders. When configuring your PBX, always store numbers in E.164 format.
Related: ENUM · CLI · A-Number/B-Number
CLI (Calling Line Identification)
The phone number displayed to the person you are calling. In business telephony, CLI lets you control which number appears on outgoing calls. You might display your main office number, a specific department number, or a local number for the country you are calling. Incorrect CLI settings can cause calls to be rejected or marked as spam by the receiving network.
Related: P-Asserted-Identity · STIR/SHAKEN · E.164
P-Asserted-Identity (PAI)
A SIP header that carries the verified caller identity between trusted networks. Unlike the standard "From" header (which can be set to anything), the P-Asserted-Identity is inserted by the provider after authentication and represents the real, verified identity of the caller. It is used for billing, lawful interception, and preventing caller ID spoofing between carriers.
Related: CLI · SIP Headers
Least Cost Routing (LCR)
A feature that automatically selects the cheapest route for each outgoing call based on the destination number. The PBX or provider maintains a table of rates from different carriers and chooses the lowest-cost option in real time. LCR helps businesses with high call volumes reduce their phone bills without manual intervention.
Related: Per-Minute Billing · Wholesale Voice · Origination/Termination
A-Number / B-Number
Telecom terms for the two parties in a phone call. The A-Number is the caller (the person making the call). The B-Number is the called party (the person receiving the call). These terms appear frequently in CDRs, routing rules, and billing systems. For example, "A-Number CLI" means the phone number shown to the B-Number.
Related: CLI · CDR · E.164
Origination / Termination
Two sides of every phone call. Origination is the process of receiving a call from the caller and putting it onto the network. Termination is the process of delivering the call to its final destination. In wholesale telecom, providers charge "origination fees" and "termination fees" per minute. When you call a mobile number, the mobile operator charges a termination fee to deliver the call.
Related: Interconnection · Wholesale Voice · Least Cost Routing
Wholesale Voice
The business of buying and selling large volumes of voice call minutes between telecom carriers. Wholesale providers offer termination services to other providers at bulk rates. Your Cloud PBX provider buys wholesale minutes and resells them to you at retail rates. The quality and cost of your international calls depend on which wholesale routes your provider uses.
Related: Origination/Termination · Least Cost Routing · Interconnection
SMS Aggregator
A company that connects businesses to mobile networks for sending and receiving SMS messages. An SMS aggregator has direct connections to multiple mobile operators and provides a single API or interface. Some Cloud PBX providers include SMS capabilities through an aggregator, allowing you to send text messages from your business number.
Related: API · ITSP
TCO (Total Cost of Ownership)
The full cost of owning and operating a phone system over its lifetime, not just the monthly subscription. TCO includes hardware (phones, network switches), setup fees, monthly subscriptions, per-minute charges, number rentals, porting fees, training, and ongoing maintenance. Comparing TCO between providers gives a more honest picture than comparing monthly prices alone.
Related: SLA · Per-User Pricing · Cloud PBX
Related Sections
📡 SIP Trunking — Trunks, channels, and provider connectivity
📞 Core Concepts — PSTN, ISDN, DID, and foundational terms
⚖️ Regulatory — Compliance, emergency calling, and data protection
🔗 SIP Protocol — SIP methods, responses, and headers
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