For my final year project, i had to combine hardware, software and communications, so i build a telephone address book, menu driven using a 2x16 LCD display.
The user could store names / numbers in the device (up to 256), and by pressing "dial" the device would connect to the telephone line and dial the number.
This was 4 yrs ago now, before this feature was build into the standard household phones. The menu system was simular to Nokia's menu system on their mobile phone address books.
It also had a radio link to a receiver that contained the telephone line interface electrronics, a PC infra-red link to allow the user to edit/add/delete on a pc as well as directly on the unit, and the names were sorted alphabeticly.
User interface on the unit was a rotory switch, and it all run from a 9V pp3 cell with a built in charger circuit when used with an AC adapter.
Most important part of a project is the documentation - so allow plent of time for this.