The Apple Watch 3 Cellular is available in two sizes —- 38mm and 42mm. ... Both the Apple Watch 3 GPS and Cellular offer the same specifications and features. The only difference is that the Watch 3 Cellular offers 4G LTE, UMTS via eSIM along with Wi-Fi (802.11b/g/n 2.4GHz) and Bluetooth 4.2 in the connectivity department.