Of particular interest are the seco

Of particular interest are the second most frequently used variants
in initial and final position which are [w] and [v], respectively. [w], and not
[f], is used initially simply because it shares two phonetic similarities with
[v], Le. the use of the lip and voicing. Informants seem to be well aware that
[f] would not be the right sound for the initial (v); otherwise there would be
no clear distinction between the two sounds.