The line is a real cellular eSIM.
Every Kelir line is provisioned as an eSIM profile from Telnyx — installed in <5 minutes via direct push (iPhone) or QR (Android), running on the cellular voice network through VoLTE. The Kelir mobile app is a control panel, never a softphone. Calls ring on the phone's native dialer. The full UCaaS feature surface — auto-attendant, IVR, hunt groups, departments — runs in the Kelir cloud and lands the call on this real cellular line.
Cellular delivery on Kelir.
Cellular delivery is what makes Kelir a different product class than RingCentral, Dialpad, 8x8, Vonage Business, and Nextiva. The UCaaS feature surface — the routing, the IVR, the hunt groups, the analytics — is comparable across the category. The line underneath is not. Every other UCaaS vendor delivers their feature set as a softphone: a mobile or desktop app that registers to a SIP server over Wi-Fi or mobile data and carries voice as packets through that connection. Kelir delivers the same feature set on a real cellular eSIM line.
Practically, that means: when an inbound call routes through the Kelir auto-attendant, hunt group, or IVR and lands on a user, the user's phone rings the way it would for a personal cellular call. The native dialer surfaces the call on the lock screen. CarPlay routes it through the dashboard automatically. Apple Watch surfaces the inbound. The Kelir mobile app does not need to be open — it is not a voice path. It's a control panel for the system: shows call history, manages voicemail, lets you change your DND, configures routing if you're an admin.
The technical mechanism is straightforward eSIM. iPhone XS and newer, Pixel 3 and newer, Galaxy S20 and newer, and most other phones released after 2018 support multiple eSIM profiles. The user's personal SIM (physical or eSIM) and their Kelir business eSIM coexist on the same phone, with iOS and Android letting them set the default for outgoing calls and SMS per app or per call. Voice runs on cellular VoLTE. SMS runs on standard cellular SMS plus A2P 10DLC for business deliverability.
What this delivery model unlocks practically: calls work without internet (no Wi-Fi or data needed), calls work when the Kelir app is suspended or has never been opened, calls work on bad signal the way personal cell calls work on bad signal, the number is accepted as a real US cellular number for 2FA SMS by banks and government services, CarPlay treats it as a regular line, and the user gets the lock-screen UI they're used to from their personal cell line.
Setup walkthrough.
Configured from Mobile app. The setup below assumes a working Kelir account and an active eSIM.
- 1
Sign up for Kelir from the mobile app or web — Solo, Team Starter, or Team Pro plan.
- 2
Pick a US business number (or submit your existing number for porting in 1–3 business days).
- 3
Confirm device compatibility — the app checks your phone's eSIM support automatically before any charge.
- 4
Provide payment method (Apple Pay, Google Pay, or card via Adyen).
- 5
On iPhone XS or newer: tap the activation link, the eSIM installs via Apple's CTCellularPlanProvisioning direct push. No QR scan needed.
- 6
On Android (Pixel 3+, Galaxy S20+): scan the QR code shown in the Kelir app from your device's Settings → Network → Add eSIM.
- 7
iOS / Android prompts you to label the line ("Work" is the default), pick the default for outgoing calls, and set ringtones. Same UI as adding any other cellular line.
- 8
The Kelir line goes live in seconds. First inbound call rings on the native dialer; outbound calls available immediately.
- 9
Configure call-handling features (auto-attendant, working hours, voicemail) from the Kelir mobile app. Multi-user routing happens at app.kelir.io for Team plans.
Where cellular delivery earns its keep.
Field contractor with bad reception
Contractor's truck Bluetooth, basement crawl spaces, rural job sites — same coverage characteristics as their personal cell line, no extra Wi-Fi-or-app failure mode. Bad signal still hurts the way bad signal hurts every cellular call. There's no extra layer.
Solo professional walking between meetings
Walks out of a coffee shop, Wi-Fi disconnects, walks past three carrier dead zones, takes a client call on cellular. The line behaves like the personal cell line because that's what it is technically.
Bank 2FA SMS code
Banking platforms increasingly block VoIP virtual numbers for 2FA. Kelir's number is a real US cellular number with native SMS — accepted for 2FA the same way the personal cell would be.
CarPlay during the drive
Inbound call to the business number routes through CarPlay automatically — same UI as a personal cell call. Hands-free is real hands-free; no softphone app fighting for audio routing.
App force-quit, phone restart
User force-quits the Kelir mobile app. Restarts the phone. Doesn't open the app for a week. Calls still ring. The line is provisioned at the eSIM level — nothing in the app is required for the line to function.
The same feature.A real cellular line.
This is the section where Kelir is structurally different from every UCaaS vendor in the buyer's reference set. The feature surface is comparable across the UCaaS category. The delivery layer is unique.
- Voice runs on cellular VoLTE — not Wi-Fi or mobile data through a softphone session.
- Native dialer rings on the lock screen — same UI as a personal cellular call.
- App suspension, app uninstall, OS update — none of it affects whether the line rings.
- Wi-Fi outages don't affect calls. Bad office Wi-Fi, dead hotel networks, basement crawl spaces — none of it matters.
- Real US cellular number — accepted by banks, payment platforms, and government services for 2FA SMS where VoIP virtual numbers get blocked.
- CarPlay, Apple Watch, lock-screen, registered Bluetooth all work natively — same behavior as a personal cell line.
- International: US number rings overseas via Wi-Fi calling on supported devices. Pair with a travel eSIM for data abroad; Kelir continues to ring on the device.
- SIM-swap resistant — eSIM has no physical card to socially-engineer at a phone store. Account changes go through admin auth in the Kelir portal.
Common questions
No. The Kelir mobile app is a control panel — it manages the eSIM, shows call history and voicemail, lets you toggle DND or change voicemail greetings, and (on Team plans) routes admins to the web portal. Calls do not happen inside the app. The Kelir app does not need to be open for calls to come through. Voice rings on the phone's native dialer (iOS Phone, Android dialer) over the cellular voice network.
No. Voice runs on cellular VoLTE, the same way a personal cellular line works. No Wi-Fi, no mobile data needed for the call itself. Internet is needed for the admin portal at app.kelir.io, the Kelir mobile app's UI (loading call history, downloading recordings), and for some carrier-rich-messaging modes of SMS/MMS.
iPhone XS or newer (iPhone 14+ in the US is eSIM-only), Pixel 3 or newer, Galaxy S20 or newer, and most other phones released after 2018 with eSIM support. The Kelir app checks device compatibility automatically during onboarding before any charge.
Under 5 minutes for most users. On iPhone XS or newer, the eSIM installs with a single tap via Apple's CTCellularPlanProvisioning direct push. On Android, you scan a QR code from the Kelir app inside your device's "Add eSIM" flow.
Yes. Modern phones support multiple eSIM profiles, and your personal SIM (physical or eSIM) coexists with the Kelir business eSIM. iOS / Android lets you set the default for outgoing calls and SMS per app or per call. Both lines ring on the lock screen, with separate notification colors and ringtones.
VoLTE is the standard voice mode on US 4G/5G networks; it's available essentially everywhere your personal cellular line gets signal. In rare areas where the carrier still uses 3G (which is being decommissioned), the line falls back to standard cellular voice. Kelir's interconnect is through Telnyx, which is a Tier-1 US carrier with full VoLTE support across the major networks.
Yes. eSIM transfer is supported from the Kelir mobile app and the admin portal — push a fresh eSIM to a new device, the old eSIM is deactivated. Useful for upgrading phones or replacing a lost device. Number portability is preserved across the transfer.
Adjacent features.
What is a business eSIM
Definition pillar — what a business eSIM is and how it works.
Cellular eSIM vs softphone
Side-by-side comparison of the two delivery models.
How activation works
End-to-end onboarding flow, device support, carrier interop.