Due to trademark issue with the name Zaptel, Digium changed the name Zaptel to DHADI (Digium Asterisk Hardware Device Interface). Asterisk 1.6.0 and later version will use DAHDI, while Asterisk 1.4 will support both Zaptel and DAHDI. Asterisk 1.2 will be unaffected by these changes.

Installing DAHDI
Download dahdi-linux and dahdi-tools from Digium's website