Yes. A smartphone can often receive GPS/GNSS signals with no SIM installed. The SIM belongs to the cellular-service side of the phone; the satellite receiver is separate.
The SIM or eSIM authenticates a subscription to a cellular network. GPS/GNSS reception determines position from satellite radio signals. Removing one does not physically remove the other.
A Wi-Fi-only tablet with suitable GNSS hardware can therefore determine satellite location without ever having a mobile subscription.
You lose normal mobile-network data and telephone service associated with that subscription. A tracking app cannot upload over LTE or 5G if the device has no cellular data connection.
Wi-Fi can still provide internet access. If there is no network at all, an app may be able to record locally and synchronize later.
Internet access can speed up or improve some parts of the positioning experience by providing assistance data and network-based location clues. This sometimes leads people to believe GPS itself requires a SIM. It does not.
Outdoors with a clear view of the sky, satellite positioning can work independently of the cellular subscription, although initial acquisition may be slower in some conditions.
Before repurposing an old handset, check battery condition, Android version, GNSS hardware and whether the tracking app supports that OS release.
LocationOf's core requirement is an Android device capable of obtaining location and running the app. For live web updates it also needs an internet path, which can be Wi-Fi rather than cellular data.
For connectivity details, see Does GPS work without internet?.
An old Android handset can make a useful dedicated logger even after you stop paying for cellular service. Before relying on it, factory-reset or clean up the device, install current system updates that are still available, check the battery for swelling or rapid discharge, and verify that the GPS receiver can get a stable fix outdoors.
Then test the exact connectivity pattern you plan to use. If the device will only upload at home, take it on a short trip with no SIM, allow it to record offline, reconnect to your Wi-Fi and confirm that the complete trip appears with sensible timestamps.
Remember that a no-SIM phone is still a computer containing accounts and location history. Use a screen lock, keep unnecessary accounts off it, and do not leave an old unsupported Android build exposed to more services than necessary.
A retired Android handset can be repurposed as a dedicated GPS logger even when you no longer maintain a SIM subscription. If it has functioning GNSS hardware, enough battery capacity and an Android version supported by the tracking app, it can record positions locally and upload them over Wi-Fi.
This setup works well for uses where real-time visibility is not essential—for example, recording a road trip and synchronizing at a hotel—or where the device spends most of its time within known Wi-Fi coverage. It is less suitable when somebody expects a constantly updating remote map far from Wi-Fi.
Before relying on an old phone, test the battery, storage, GPS reception and background behavior. A five-year-old device that reaches a good satellite fix may still be a poor dedicated tracker if its battery shuts down after an hour.
Removing the SIM changes cellular connectivity; it does not erase the device's accounts, Wi-Fi connections, serial number, app data or locally recorded location history. A no-SIM phone should still be treated as a computer containing potentially sensitive information.
Use a screen lock, remove accounts the dedicated logger does not need, keep the operating system as current as the hardware allows, and avoid installing unnecessary software. If the phone is too old to receive meaningful security updates, limit what accounts and private data you keep on it.
For a lost handset whose SIM has been physically removed by somebody else, see Can you find a phone after the SIM card is removed?.
LocationOf does not need a telephone number in order to obtain Android location. The practical requirements are that the device can run the current app, has the required location permission, can obtain useful location data, and eventually has an internet connection if you want those points to appear on the LocationOf website.
That internet connection can be Wi-Fi. If the phone will regularly spend hours away from Wi-Fi, test how the app handles local storage and later synchronization. Also verify background operation with the screen locked, because removing the SIM does nothing to exempt an app from Android's background and battery rules.
Continue with Android background location and battery optimization for trackers.