Guitar playing BoostApps reader War Machine discovered this app and recommends it for all guitarists.  It's an app and game that helps you learn the notes on the fretboard for the guitar and other stringed instruments like the banjo or bass.  It also has a guitar tuner.

This a demo.  It doesn't expire but some of the features are limited:

• Only the first 7 frets can be used.
• The training mode can only be used for 3 minutes per session.
• The game mode is limited to the first 4 levels.
• Statistics and preferences aren't saved between sessions.
• However the tuner is fully functional

Type: Demo
Vendor: MobileTutor - Product Page, Help
Data Connection Required: No
Minimum Java ME profile: MIDP 2.0
Screen Size:
Boost CDMA Compatible: (tested on Motorola Rambler): Yes
iDEN Compatible: (tested on i776):  Yes
Supported Boost Phones: All (Incognito, Rambler, Seek, Rant, Mirro, Juno, Factor, i856, etc.)

If you are a musician here's an app for you.  Maestro  offers three functions; tuner, pitch pipe and metronome.

Type: Freeware
Author: Andy Judge
Data Connection Required: No
Supported iDEN phones: All Falcon Series (i776, i465, i9, i290, etc.)