I started as a Guitarist with a Gibson Heineken Special Epi, then switched to bass with my Dean standard 4 string Bass. I call myself a bassist because its what i prefer to play, and its what I play in my band.
Nobody wanted to play bass, and if i didnt pick it up, we'd have 3 guitarists, drummer, and vocalist. So, me being me, decided i wanted to be that one guy to switch to bass. Im actually better at bass than i am at guitar.