Your Onoff calls go over the internet (VoIP) by default. When the internet connection is too weak, they can go over the regular mobile network (GSM). This article explains both modes and when each applies.
The two modes
| VoIP (default) | GSM | |
|---|---|---|
| Network | Wi-Fi or mobile data (4G/5G) | Mobile network, through your phone's SIM card |
| Cost | Based on your Onoff plan, no roaming fees | Your mobile operator's rates, including roaming |
| Several devices | Yes, up to 3 | No, one phone only |
| Without internet | No | Yes |
To choose the mode, turn the Call via Wi-Fi/data option on or off in the app.
The GSM mode described here is different from Onoff Calls, which uses another technology. See "Onoff Calls: receive your calls over the mobile network".
Which mode to use
| Situation | Recommended mode |
|---|---|
| Good Wi-Fi or 4G/5G connection | VoIP |
| Weak internet but good mobile signal | GSM |
| Travelling abroad | VoIP, to avoid roaming fees |
| Several numbers on one phone | VoIP |
How VoIP works
Your voice is converted into data, sent over the internet in small packets, then played back to the other person in near real time. This is what lets you use the same number on several devices, call from abroad without roaming and assign numbers without SIM cards.
For good call quality
- Use a stable Wi-Fi or 4G/5G connection.
- Avoid large downloads or streaming during calls.
- Keep the app up to date.
Recognized mobile numbers
Onoff numbers are real mobile numbers, recognized by operators and most services: bank verifications, two-factor authentication codes, apps, delivery services. See "Receive SMS from special services".
Security
All Onoff communications are encrypted.
Related articles
- Onoff Calls: receive your calls over the mobile network
- Gateway numbers
- Web app call preferences
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