This wiki describes work within the Osmocom community to develop E1/T1 hardware interfaces.
E1/T1 lines were pretty common in the 1990ies and up until about 2010, as they built the heart of many connections to the digital, circuit-switched telephony (ISDN) network.
Today (2019), E1/T1 are mostly only found in connection with GSM base stations (BTS), where the Abis interface of a BTS is still officially only specified over E1/T1.
Hardware for connecting E1/T1 to a (Linux) computer has always been expensive, and is rather difficult to find. Also, it only comes in PCI and PCIe form-factor, making it unsuitable to many popular embedded Linux platforms (whether ARM or x86) which don't feature such interfaces.
We've been wokring on creating E1-USB adapters based on a variety of approaches, see further wiki pages for details.