That is a Lucent DSP UnderRFShield that provides CallerID, DTMF, modem, and speaker phone potential.

Thought to be a DSP1653 see the schematics directory http://www.TuxScreen.net/download/schematics/

• http://www.bdti.com/procsum/dsp16xx.htm
• http://www.bdti.com/products/reports_bg99.htm
• http://www.e-insite.net/ednmag/index.asp?layout=articlePrint&articleID=CA46694
• FlashDSP1650 Data Sheet

Here are some UndocumentedDSPFunctions.

Perhaps a Linux Telephony driver should be written?

http://www2.linuxjournal.com/lj-issues/issue82/4468.html