Short answer
Virtual telephony takes each call through six layers: a number from the national plan, an operator that delivers it over VoIP or a SIP trunk, a cloud phone system, opening-hours and distribution rules, the device where it rings, and the record. In Spain, a geographic number requires an address in its province, porting is activated within one business day of the agreed date and 112 is free.
Key verification: Call from an external mobile and check which layer the call stops at when it does not ring.
Sources and limitationsVirtual business telephony replaces the physical line and the phone system in the comms cupboard with services that run over the network: a number from the Spanish national numbering plan, an operator that delivers calls over the internet (VoIP or a SIP trunk), a cloud phone system that applies call routing rules, and apps on the computer or mobile where calls are answered. The clearest way to understand it is to follow an incoming call through six layers: number, operator, phone system, rules, device and record. Each layer decides something different and fails in a different way.
The path of an incoming call
The table works as a diagram: read it from top to bottom, in the order the call travels.
| Step | Layer | What happens |
|---|---|---|
| 1 | Number | The customer dials a number from the national plan: geographic, mobile, national or freephone |
| 2 | Operator | The public network delivers the call to the number's operator, which converts it into voice over IP |
| 3 | Cloud phone system | Identifies which company and which number the call belongs to |
| 4 | Rules | Applies opening hours, greeting, menu, queue, ring group or forwarding |
| 5 | Device | Rings the app or phone of the available agent |
| 6 | Record | Stores the call detail, the recording where applicable and the activity in the CRM |
What each layer decides and what can go wrong
| Layer | What it decides | What can go wrong |
|---|---|---|
| Number | How customers find you and what cost the caller perceives | Incomplete documents, number not activated, unsuitable type |
| Operator | Routing, porting and access to emergency services | Delayed porting, calls that do not get through from some networks |
| Phone system | Users, licences, associated numbers and permissions | Number not assigned to any call flow, expired licence |
| Rules | Who receives each call and when | Wrongly configured hours or bank holiday, queue with no exit |
| Device | Where calls are answered and at what quality | App that does not ring, choppy audio, saturated Wi-Fi |
| Record | What is stored and who can see it | Calls without a CRM record, recordings without prior notice |
Number: geographic, mobile, national or premium rate
The number is the only layer the customer sees and the most heavily regulated. The choice between geographic, national, mobile, freephone or premium rate is covered in the guide to choosing your company's number; what matters here is how it shapes the rest of the system.
A relevant rule changed in 2026. A resolution of Spain's Secretary of State for Telecommunications published in the BOE, the official state gazette, on 30 April 2026 abolishes geographic nomadic numbering, keeps nomadic services on code 51 and requires subscribers to the fixed telephone service to have a legal address in the province of the geographic numbering they use and to prove it to their operator. It allows six months of transition from its entry into force (Resolution of 27 April 2026, BOE-A-2026-9431). In practice, a Málaga geographic number requires an address you can prove in the province of Málaga.
For Spanish fixed numbers, CloudTalk states a service address in the same city as the number or, as an alternative, the CIF tax ID and a company registration in that city, with a lead time of 1 to 5 business days; those numbers do not support SMS (CloudTalk numbering requirements, consulted on 22 October 2026).
VoIP operator, SIP trunk and cloud phone system
With an all-in-one cloud phone system, the same provider supplies numbers, operator and phone system: you buy licences and numbers in a single account. With a SIP trunk, an operator delivers your lines as voice over IP channels and you connect them to your own phone system, in the office or on a server. A SIP trunk gives more control and obliges you to maintain the phone system; the integrated model is simpler, but leaves numbering and rules in the hands of a single provider.
When something fails, in the integrated model you open a single ticket; with a SIP trunk you need to know whether the problem lies with the operator or with your phone system. The cost of each option is calculated in the guide to the cost of a virtual phone system.
Apps: where the call rings
A softphone on the computer, a mobile app or a desk IP phone are different ways of registering with the same phone system. The choice between the provider's own app and an external SIP client is covered in native softphone or SIP client. If what you need is to separate your personal and business phone on the same mobile, the guide to virtual number or eSIM distinguishes the mobile line from the shared number.
Porting, emergencies and connection quality
Porting. Article 70 of Spain's General Telecommunications Act, Law 11/2022, recognises the right to keep your number when changing operator: geographic numbers at a fixed location and non-geographic numbers at any location. The number must be activated within one business day of the agreed date, loss of service must not exceed one business day and the receiving operator leads the process (Law 11/2022, consolidated text). The CNMC, Spain's markets and competition regulator, sets the conditions for keeping numbers by circular (porting at the CNMC). Step-by-step procedure: keeping your landline number when changing phone system.
Emergencies and location. Article 74 of the same Act requires operators of number-based services to route calls to 112 free of charge and to give emergency services the location information that a royal decree specifies. If the agent answers from home or while travelling, the location associated with the line may not match theirs. Ask the provider in writing whether each app can call 112 and which address is transmitted, and do not make test calls to 112.
Connection quality. Voice over IP depends on the local network. CloudTalk warns that VoIP does not tolerate packet loss and recommends a wired connection where possible and prioritising voice with QoS on the router (CloudTalk call quality guide). If you already have dropouts or echo, follow the VoIP audio diagnosis.
Fictional example: a five-person small business moves to the cloud
A fictional accountancy firm in Málaga has five staff, a geographic number with two simultaneous channels and a physical phone system with five desk phones. It wants staff to work from home two days a week.
| Layer | Before | After | What it checks |
|---|---|---|---|
| Number | Geographic number on the landline | The same number, ported to the cloud provider | Address proven in the province and porting date |
| Operator | Landline operator | The provider's VoIP operator | Incoming calls from several networks |
| Phone system | Physical unit in the office | Cloud account with five users | That the number is linked to the correct call flow |
| Rules | Manual forwarding when leaving | Opening hours, bank holidays and voicemail with email alert | Simulated out-of-hours call |
| Device | Five desk phones | Three softphones and two mobile apps | That they ring with the screen locked |
| Record | No useful history | Call history and activity in the CRM | That the test call appears in the customer record |
In its peak hour it receives 18 calls averaging 4 minutes and makes 6 of 5 minutes: 18 × 4 + 6 × 5 = 72 + 30 = 102 minutes of conversation in 60 minutes, that is, 102 ÷ 60 = 1.7 simultaneous calls on average. With only two channels, any peak above the average leaves customers hearing an engaged tone. Before migrating, the firm asks whether the new service limits simultaneous calls per number or per account, because that figure replaces the two channels of the old line.
Checks after the switch
- Number: call from a mobile on another network and from a landline.
- Operator: the provider confirms in writing the date porting was completed.
- Phone system and rules: an out-of-hours call reaches voicemail and triggers the alert.
- Device: each person receives calls with the mobile locked and with the computer asleep.
- Record: the test calls appear in the history and in the CRM with the correct number.
- Emergencies: you have in writing how the provider handles 112 and the location of each app.
Sources and limitations
Documentary review: . Content type: Conceptual guide.
Linked sources describe the terms and capabilities each provider publishes. Examples that use fictional data are labelled in the text.
- Resolution of 27 April 2026, BOE-A-2026-9431www.boe.es
- CloudTalk numbering requirementshelp.cloudtalk.io
- Law 11/2022, consolidated textwww.boe.es
- porting at the CNMCwww.cnmc.es
- CloudTalk call quality guidehelp.cloudtalk.io
Official sources, explained calculations and clearly labelled examples. Read about our methodology and use of AI in writing.