The ThinkPad T480 can function as a fully featured mobile phone with calls, SMS, and mobile data. The laptop includes a SIM slot for LTE modems, but PCM pins for audio are unconnected. However, a bug in the Intel Management Engine allows flashing Libreboot instead of stock firmware, removing the wireless card whitelist.

A suitable modem is the Quectel EG25-G, used in the Pine Phone and featuring an ARM core running Android. Custom firmware with free software userspace registers the modem as a USB audio interface for call audio. SMS and mobile data work out of the box.

M.2 versions of the EG25-G are rare and have incompatible antenna connectors, requiring finicky conversion cables. Once configured, you can replace your mobile phone entirely and even run Android apps natively via Waydroid.