Multi-SIM proxies: how they work and what the drawbacks are

The term has no single definition. Providers use it in two different ways:

• A device with many SIMs: multi-slot modems, 4G dongles on a USB hub or SIM banks. Each SIM becomes a proxy, but they all share the same box, the same power supply and the same management connection.
• A rotating pool of SIMs: a single address (gateway) you connect to, which sends each connection or each rotation out through a different SIM in the pool, often from another carrier. To keep the same IP longer there's usually a “sticky” mode tied to a session ID.

Either way the final IP belongs to a mobile carrier, so it's still a mobile proxy. What changes is how the SIMs are managed, and that's exactly where the differences come from.

A modem with many SIMs costs less than lots of phones and takes up less space: for anyone running thousands of lines that's a real saving. A rotating pool also gives you ever-changing IPs without having to think about rotation: useful for collecting large volumes of public data, where every request is independent and there's no account to protect.

• IPs that switch carrier and city. When rotating across different SIMs, the site sees the user jump from one carrier to another (different ASNs) and sometimes from one area to another. For an account that's unusual behaviour that triggers checks. The reasoning is in IP rotation.
• Interrupted sessions. Without sticky mode each connection may leave through a different SIM: logins, carts and payments break halfway. With sticky mode, how long it lasts depends on the provider's rules, not on you.
• SIMs shared within the pool. In rotating pools the same SIMs serve many customers at the same time: the IPs' reputation also depends on what everyone else does.
• IoT or roaming SIMs. Some setups use Internet-of-Things data SIMs or foreign SIMs on roaming. When roaming, traffic usually exits in the country of the carrier that issued the SIM: a German SIM used in Spain shows a German IP. The IP's country isn't the one you expect.
• One fault takes down many proxies. When many SIMs sit in the same box or on the same USB hub, a reboot, a power dip or an antenna problem brings several proxies down together. And cheap modems are often 4G only.
• The device fingerprint. A site doesn't just see the IP but also the traits of the network packets. If the provider doesn't let you choose them, you risk a fingerprint that doesn't match your browser: more in TCP/IP fingerprint.

1. Ask whether the proxy is a dedicated device or a pool, and how many people use it alongside you.
2. Check carrier and country before and after a rotation with the IP reputation tool: if the ASN changes every time, you're leaving through different SIMs.
3. Check how long sessions last: open the same site several times and see whether the IP stays the same until you change it.
4. Ask whether the network is 5G or 4G and whether you can choose the TCP/IP fingerprint.
5. Run the full test (IP, DNS, WebRTC, timezone) described in How to test a proxy.

Every ProxyHub proxy is a dedicated 5G smartphone with its own SIM from a local carrier (TIM, Vodafone, WindTre and Iliad in Italy; plus the Netherlands, the UK, France and the United States). When you change IP, the phone reconnects to the network: the new address arrives within seconds from the same carrier and the same country, and between changes the IP stays yours.

On top of that you pick the TCP/IP fingerprint in the client area, you get IPv4 and IPv6 and unlimited traffic. It's the setup closest to a real user on their own phone: the one you need for accounts, verifications and ongoing work.