I Just Called To Say I Love You by Stevie Wonder is in Gb at 100 beats per minute and runs 3:02 across 52 bars. It uses 10 chords — Db, Ebm, Ebm7, Ab, Bbm, Bbm7, Ab7sus, Ab7, and a few more. The chord diagram changes as the song plays and the words light up as they are sung, so you can strum and sing along without reading ahead.
Want the melody line note by note? I Just Called To Say I Love You guitar melody tab.