Business VoIP for SMEs: Teams Phone, KPN, 3CX and RingCentral compared (2026)

ISDN switched off: why every SME now uses VoIP

KPN switched off the ISDN network in 2019, followed by other Dutch providers. Since then, business telephony is exclusively available via VoIP: calling over the internet. For SMEs still running a legacy IP system or planning to switch, there are four practical routes. The choice depends on three factors: are you already using Microsoft 365, do you need a fixed line with a local area code, and how many concurrent calls do you expect? This article compares the four most widely used solutions on cost, features and GDPR compliance.

Microsoft 365 users

Microsoft Teams Phone: calling, meetings and chat in one platform

Microsoft Teams Phone is the natural choice for SMEs already using Microsoft 365. Teams Phone Standard is an add-on (approx. EUR 8/user/mth — verify at microsoft.com) that adds PSTN calling to the Teams platform you already use daily for meetings and chat. Numbers are ported via a Microsoft Calling Plan or via Direct Routing through a Dutch SIP provider such as KPN, T-Mobile or Odido. EU Data Boundary ensures calls and recordings are processed in Amsterdam or Dublin (verify scope at the Microsoft Trust Center). EU AI Act Art. 4 applies if you enable Intelligent Meeting Recap or transcription — ensure an internal AI literacy policy is in place.

• Cost: M365 Business Basic approx. EUR 5.25/user/mth + Teams Phone Standard add-on approx. EUR 8/user/mth. Verify current prices and available Calling Plan bundles at microsoft.com.
• Features: PSTN inbound and outbound calls, call transfer, queues, auto attendant (IVR), call recording, transcription (AI-powered), 300 participants per meeting.
• When to choose: Ideal if you already have M365 Business Basic, Standard or Premium; minimal additional hardware investment; integrates with Outlook calendar for scheduling.

Fixed line with local number

KPN / Odido IP-Flex: managed fixed line with local area code

KPN (Hosted Bellen), Odido (IP-Flex) and T-Mobile Business offer a Hosted PBX service for SMEs: a fixed line over internet with a local area code, fully managed by the provider. No own servers; the PBX runs at the provider's side. Devices are IP phones or softphones (app on PC/smartphone). Suitable for businesses that want to retain a professional fixed line with a local area code without running their own servers. Prices depend on the number of lines and call minutes — verify current rates at KPN.nl or Odido.nl. Calls are processed on Dutch servers and providers are regulated by the ACM (Dutch telecommunications regulator).

• Cost: Indicative, depends on line package and call minutes; verify current business telephony packages and installation costs at KPN.nl or Odido.nl.
• Features: Local area code (010, 020, 040 etc.), call forwarding, queues, IVR, voicemail-to-email, mobile pairing, caller ID.
• When to choose: Ideal for businesses with a reception desk needing a professional local number; suitable for teams without existing Microsoft 365 licences.

Open-standard PBX

3CX: free open-source PBX for up to 10 concurrent calls

3CX is an open-standard IP-PBX based on the SIP protocol, available as a hosted cloud version or self-hosted on Windows/Linux. The Free plan supports up to 10 concurrent calls with no licence costs — you only pay for the SIP trunk (the telephone connection from a Dutch provider such as SpeakUp, Voys or Sipcall). The web client, mobile apps (iOS/Android), Microsoft Teams integration and basic call queues are all included in the Free plan. For more concurrent calls or advanced features (call centre, CRM integration), paid SMB and ENT licences are available (verify at 3cx.com). 3CX requires more technical setup than a hosted solution but gives maximum control over data storage and your dial plan.

• Cost: Free plan: no licence costs for ≤10 concurrent calls. Pay only for SIP trunk (approx. EUR 5–15/line/mth at SpeakUp/Voys/Sipcall — verify with provider). SMB/ENT licences for more features: verify at 3cx.com.
• Features: Web client, iOS/Android apps, voicemail, queues, call recording, Teams integration (Free), IVR (paid), CRM integration HubSpot/Salesforce (paid).
• When to choose: Ideal for technically skilled SME teams or IT firms wanting to minimise costs and retain full control over their telephony environment.

UCaaS for larger teams

RingCentral: cloud UCaaS with CRM integrations for growing SMEs

RingCentral (RingEX, formerly Unify Office) is a fully managed cloud UCaaS (Unified Communications as a Service) combining calling, meetings, chat and fax. The platform offers out-of-the-box integrations with Salesforce, HubSpot, Zendesk and Microsoft 365 — attractive for SMEs with CRM-driven sales processes. Price approx. EUR 19–29/user/mth depending on plan (verify at ringcentral.com for current Dutch-market pricing). PSTN calling is included for Dutch numbers; international bundles are available. GDPR: RingCentral Inc. processes data in EU regions; verify the RingCentral GDPR statement and sign a Data Processing Agreement (DPA) per Art. 28 GDPR.

• Cost: Approx. EUR 19–29/user/mth (verify current NL pricing and annual discount at ringcentral.com). PSTN calling included; international bundles extra.
• Features: PSTN calling, meetings up to 200 participants, team chat, fax, AI transcription, call analytics, CRM integrations (Salesforce, HubSpot, Zendesk), IVR, queues.
• When to choose: Ideal for sales or service teams actively using CRM (HubSpot/Salesforce); growing SMEs wanting multiple communication channels in one platform.

Side-by-side comparison

GDPR and call recording: what are the rules?

Business VoIP systems make call recording technically simple, but GDPR imposes strict conditions. Calls contain personal data (name, contact details, sometimes health or financial information) and fall under the General Data Protection Regulation.

• Legal basis for recording: Art. 6(1)(a) consent (inform the caller and obtain consent, typically via a spoken message at the start of the call) or Art. 6(1)(f) legitimate interest (documentation or quality control — harder to justify for B2C calls).
• Transparency obligation Art. 13 GDPR: inform callers about the recording, its purpose, the retention period and their rights (access, objection, erasure) via the spoken message or your privacy statement.
• Retention period: do not retain recordings longer than strictly necessary for the stated purpose; 30–90 days is common for quality control (verify with your privacy counsel).
• Data Processing Agreement (DPA): sign an Art. 28 GDPR processing agreement with your VoIP provider if they have access to call data. All four providers above offer a standard DPA.
• Dutch Telecommunications Act Art. 11.7: even in a business context (B2B), you may not record calls without informing the caller; the spoken notice at the start of the call ('this call may be recorded') is sufficient.

Number portability: keeping your existing phone number

When switching to a new VoIP provider you can retain your existing phone number via number portability. The procedure: request portability from your new provider; the new provider arranges the transfer with your current provider via the ACM-regulated portability process. The transfer takes approximately 5–10 business days; during migration you can remain reachable via both systems. Inform your clients of your number in advance and consider listing a temporary mobile number on your website.

Frequently asked questions

Does my business still need a fixed telephone line?

A fixed line is not legally required, but a local area code (010, 020, 040 etc.) projects a professional image and improves accessibility for clients who avoid mobile numbers. With VoIP you can link a local number to softphones or mobile apps — no physical device at the office. If you work fully mobile and clients call you directly on mobile, you can drop the fixed line.

Can I keep my existing phone number when switching to VoIP?

Yes. Number portability is legally mandated by the ACM (Dutch Authority for Consumers and Markets). You request portability from your new VoIP provider; they arrange the transfer with your current provider. The transfer takes approximately 5–10 business days. Keep your number documentation and check whether your current contract has a notice period before starting the portability request.

Does VoIP work with a poor internet connection?

VoIP calls require a stable internet connection with a minimum bandwidth of approximately 100 kbps per concurrent call (uplink and downlink). A poor connection can cause delay, jitter or dropped calls. Use a wired connection over Wi-Fi for business-critical calls. Setting QoS (Quality of Service) on your router prioritises VoIP traffic above other data transfers.

Do I need a Data Processing Agreement (DPA) with my VoIP provider?

Yes, if your VoIP provider has access to personal data in calls or recordings — which is the case for most hosted services. This requires a processing agreement under GDPR Art. 28. Microsoft (Teams Phone), KPN, 3CX and RingCentral each offer a standard DPA in their contract documentation. Check that the DPA uses EU standard contractual clauses (SCCs) for data transfers outside the EEA.

What does business VoIP cost for an SME with 5 users?

A rough indication for 5 users: Teams Phone add-on approx. EUR 40/mth (5 × EUR 8, excluding M365 licence and Calling Plan bundle); 3CX Free with SIP trunk approx. EUR 25–75/mth (5 SIP lines from a Dutch provider); RingCentral approx. EUR 95–145/mth (5 × EUR 19–29). Compared to a traditional ISDN PBX (one-off EUR 1,000–5,000 plus monthly line costs), switching to VoIP is in most cases cheaper over time. Verify current rates with the respective providers.