Is it possible to get a device's telephony ID, MAC Address, serial number, and/or Android ID through a mobile website?
That is, not through a downloadable app, but through a link that the user goes to in the browser on their mobile device?
If so, how?
No, this is not possible. Even for native apps, device identity information is safeguarded behind the READ_PHONE_STATE permission.
As websites cannot request permissions, you cannot retrieve this information outside of an app.