Asterisk is an Open Source PBX and telephony toolkit. It is, in a sense, middleware between Internet and telephony channels on the bottom, and Internet and telephony applications at the top.

Asterisk includes a set of standard sound files in various formats. The core part of that collection in US English, by voice actress Allison Smith, is contained in various encodings in packages asterisk-core-sounds-en-*; this package registers these through the alternatives system to provide the default "en" (English) and "en_US" (USA English) sounds.