OnSIP

OnSIP is a configurable business phone system combining SIP calling, browser access, and desktop and mobile apps. It fits teams that need custom call handling, multiple business numbers, and CRM connections, particularly when administrators want to adjust users and features as staffing changes. The main decision is whether the chosen plan’s calling and messaging terms match how your organization communicates.

Overview

OnSIP has operated since 2004 and is headquartered in Sunnyvale, California. Its month-to-month billing lets a business pay for the users and features it needs, then add or remove them as requirements change. The Admin Portal brings setup, real-time feature edits, payment management, contact management, and invoices into one control point, which is useful for organizations that do not want a fixed, all-or-nothing phone deployment.

The free service allows up to 100 users and unlimited extensions, but those accounts cannot dial regular telephone numbers. Paid plans provide the SIP-to-PSTN gateway needed for ordinary phone-number calling. That distinction makes the free tier best suited to SIP-based internal use or evaluation rather than as a complete public-facing phone service.

Key features

• Call workflows: Multiple business numbers, custom call routing, and an auto attendant support reception and departmental call flows. Voicemail transcription lets users review messages as text instead of listening to every recording.
• Apps and device reach: Apps cover Windows, Mac, iPhone, and Android, while the browser softphone works in Chrome, Firefox, and Opera. One SIP address can remain registered on up to 10 devices, practical for users who switch between desk, desktop, and mobile calling.
• Security: Softphone apps provide end-to-end encryption, and desk-phone encryption is also supported. When both parties use the OnSIP app, professional call-link media uses DTLS SRTP encryption.
• Integrations: HubSpot, Odoo, and Zendesk connections are included with the free plan; an Open API is also available among the CRM integrations. This gives teams already using those systems a useful starting point without immediately buying an integration package.
• Conferencing: Web and desktop video conferences accommodate up to five people. Audio conference suites handle up to 15 simultaneous callers, so larger meetings need a different arrangement.
• Administration and support: Users and features can be changed independently, and OnSIP says its knowledge base contains setup articles, instructions, and video walkthroughs built over 20 years. Gartner Digital Markets has awarded it a Best Customer Support badge for four consecutive years. The platform can also be used by businesses working toward HIPAA obligations.

Pricing

OnSIP offers a free plan, paid service from $18.95/user/mo, and a 30-day trial. Month-to-month contracts are available.

The Free Plan is a fit for large SIP communities that do not need calls to ordinary numbers. Unlimited is the clearer starting point for a small team that needs PSTN access and messaging, but its five-user minimum and 250-message account allowance matter for very small or high-volume groups. Basic suits organizations that need defined attendant, ring-group, voicemail, and recording capacity, while its exclusion of calling minutes and messaging can raise the effective cost. Pay-as-you-go is better for variable usage than a bundled-minute plan, provided the account-level charge and separate call costs fit the budget.

Platforms

OnSIP supports Android, iOS, macOS, Windows, and web access. The browser softphone supports Chrome, Firefox, and Opera. SIP addresses can be active on up to 10 devices.

Who it's for

OnSIP is strongest for growing businesses that need configurable routing, several business numbers, auto-attendant menus, and CRM links while retaining administrative control over users and features. It also suits teams that value encrypted app calling and need a path toward HIPAA-related obligations. It is a poor fit for a free service expected to place ordinary telephone calls, and teams with larger video meetings should note the five-person video limit.

Pros and cons

Pros

• Free plan supports up to 100 users with unlimited extensions.
• Custom routing, auto attendant, voicemail transcription, and multiple numbers cover complex business call flows.
• Free HubSpot, Odoo, and Zendesk integrations can reduce initial setup friction.
• Month-to-month contracts and adjustable users and features suit changing headcount.
• Apps, browser calling, 10-device registration, and encryption support flexible deployments.

Cons

• Free SIP accounts cannot dial regular phone numbers.
• Unlimited requires at least five users and limits SMS/MMS to 250 per account.
• Basic and Pay-as-you-go list no included calling minutes; Basic also excludes messaging.
• Video conferences top out at five participants.

Alternatives

Microsoft Teams is a better choice when free group meetings for up to 100 participants, 60-minute limits, and 5 GB of cloud storage matter more than a dedicated phone system.

3CX suits organizations wanting a free tier capped at 10 users and four simultaneous calls, with annual manual license renewal.

PortSIP PBX is an alternative for teams considering self-hosted or API-capable deployments; its free edition allows up to two simultaneous calls and three extensions.

VitalPBX is worth considering for a free community edition with 12 extensions and two VitXi WebRTC clients.

Zadarma offers a free Standard plan with five users, four voice menus, and 200 MB of storage.

Freshcaller fits teams seeking a free agent plan billed per minute, with unlimited agents, or a Growth plan at $15.00 per month billed annually.

Talkroute is a paid alternative with a Basic setup of one user, one number, one mailbox, and 500 text messages per month.

CallHippo may suit a buyer wanting a free Basic period for six months before moving to paid plans.

Verdict

Choose OnSIP for a configurable, app-based business phone system with strong user administration, routing controls, and CRM integrations. Its free tier is unusually broad for SIP users, but organizations needing regular-number calling must budget for a paid plan and examine included minutes, messaging, and minimum seats carefully. Look elsewhere if large video meetings or straightforward bundled calling costs are central requirements.