有可能官话的 w 演变成吴语的 v。不能说明当时官话的w已经变成v。
(1) 微母: 中古 *ɱ > 元代官话 *v (==> 借入吳語 /v/. For instance, 尾: 上海文讀
vi vs. 白讀
mi).
(2) 疑母, 影母, 喻母, 匣母: 中古 *ŋw, *ʔw, *jw, *ɣw > w. (cf. 温州: 危 ńy, 汪 uɔ, 王 ɦyɔ, 丸 ɦy).
According to this article (
http://www.pkucn.com/forum.php?mod=viewthread&tid=36461&page=2 cited by YangMuye):
(1) + (2) = 微母/V/ + 其他聲母/W/ → /V + w/ + /W + v/ → /W + v/ → Beijing /W/ (Note: 元代仍然有独立的微母, 明代晚期微母已并入影母
http://zh.wikipedia.org/wiki/微母). And now the Beijing dialect is undergoing a new development ("城区正在经历一次新的演变过程"): /W/ → /W + v/ → /V + w/.
To sum up,
微母/V/ may come from:
(1) Beijing dialect as a result of a new sound change: w > v
(2) Other Mandarin dialects (e.g., 西安) as a result of 中古 *ɱ > v (without going through /w/. "中古微母至今在西安话中保留 V 型发音,而影疑喻(云)三母这一类字使用 W 型发音.").
(3) Other Chinese languages as a result of borrowing
疑母, 影母, 喻母, 匣母/V/may come from:
(1) Beijing dialect as a result of a new sound change: w > v
(2) 山西 Mandarin dialects as a result of 微母/V/ + 其他聲母/W/ → /V + w/ → /V/ (
http://www.pkucn.com/forum.php?mod=viewthread&tid=36461&page=2).
the same girl, almost in a row, pronounces the name Wang in two different ways: with initial /w/ sound and with initial /v/ sound. Am I going nuts?
Obviously, the speaker is treating /w-/ and /v-/ as
free allophones for the same word
Wang (it is thus not "conditioned" by the vowel). In the Beijing dialect, /w-/ and /v-/ are treated by some as free allophones and by others as conditioned allophones ("有的人将它用成自由变体,有的人将它用成条件变体"
http://www.pkucn.com/forum.php?mod=viewthread&tid=36461&page=2). So what you heard is probably a feature specific to the Beijing dialect. She doesn't seem to be a Wu speaker because 王 (喻母) is pronounced as ua_̃ (上海), ɦua_ŋ (蘇州), or ɦyɔ (温州) in the Wu language.