OpenBTS is an implementation of the GSM air interface (Um) that allows cellular handsets to be used directly as SIP endpoints. It uses a software-defined radio to generate its air interface and uses Asterisk or yate as its network interface.
OSERL (Open SMPP Erlang Library) is an erlang implementation of the Short Message Peer to Peer protocol, covering the entire specification (version 5.0).
Forward and backward compatibilities guidelines were adopted.