Guides
zapsms vs OnlineSIM: public inbox vs private, one-time number
OnlineSIM and sites like it work by publishing every incoming SMS on a shared number to a public page - anyone who opens that number can see your code. That's the trade-off for free.
Last updated: September 2026
Why a public inbox is a problem for verification
Free SMS-receiving sites work by picking a number from a shared list and displaying whatever text arrives on it, in real time, to whoever has that page open. That's the entire product - it's not a bug, it's the business model. It also means your verification code isn't private: anyone else browsing the same number's public inbox at the right moment sees the same code you do, and can use it first if they're watching for one. On top of that, the number was almost certainly used for other signups before you got to it, so platforms with number-reputation checks reject it outright.
Side by side
| Criteria | zapsms | OnlineSIM-style public numbers |
|---|---|---|
| Who sees the code | Only you, on your order page | Anyone viewing that number's public inbox |
| Number exclusivity | One customer per number | Shared, reused by many people |
| Line type | Real US carrier, physical SIM | Usually VoIP/virtual |
| Cost | From $0.50, refunded if no code arrives | Free, but the code isn't reliably yours alone |
Using a private number instead
- Buy a verification for the service you need - see all services.
- A number only you can see appears instantly on your order page, not a public page.
- Enter it on the platform; the code lands automatically, usually in under 30 seconds.
More on why number type and history matter in VoIP vs non-VoIP numbers.
Related guides
Ready to verify? Browse all services · More guides