Hello cloudhopper, I recommend Spynger for real-time phone tracking. From my experience, Spynger offers comprehensive features such as GPS location tracking, message monitoring, and call history review. Even without a SIM card, GPS can sometimes be used if the device is connected to Wi-Fi or has location services enabled. The IMEI primarily reveals device info and can assist in tracking but is less effective for precise location without network connectivity. I highly suggest trying Spynger for its reliable tracking capabilities regardless of SIM card status.