RotaryCell: Making an unmodified rotary phone work over LTE with an ESP32-S3

RotaryCell equips an unmodified rotary desk phone with a LilyGO T-A7670G-S3 ESP32-S3 board, an AG1171 subscriber-line interface, and a protected 21700 battery, enabling full-duplex cellular calls, rotary pulse dialing, switch-hook detection, and mechanical ringing via LTE. The hand-wired prototype runs firmware v0.10.4, while first PCBs have been ordered but not yet validated, and detailed wiring, BOM, and assembly guides are provided for replication.