Generally, when you encounter a kalimba, it is usually in a particular key. The Alto usually comes in G major. The Bb Treble comes in Bb. The 17-Note African-tuned karimba comes in A (unless we retune it), and the 15-note karimba (aka mbira nyunga nyunga) comes in F.
One usually plays a G major kalimba in G; but there are other ways. You can actually pick a different note on the kalimba and make that one be the root note. You establish a particular note as the root note by emphasizing it as "home base." You can emphasize a note as "home base" by starting or ending a song on that note, or by playing it more often that the other notes.
If you use an alternative note (not the key note of the kalimba) as the root note, then you are playing in a different "mode" than the one suggested by its original key. The different modes have different scales, each with its unique melodic flavor.
In a noteworthy twist, traditional karimba music uses different modes in the same manner that western music does. What makes this remarkable?