Any computer could make a phone call; having a handler in place for "tel:" is certainly the first step (but not even really necessary!) No amount of probing whether this is a mobile device, or has a SIM card, or has properties of Android or whatever, is going to generously include all devices that are capable of placing PSTN calls.<p>I mean, yeah, check and see whether it has a microphone and audio output - that's fairly mandatory for telephony operations. Other than that... dunno.