Do some (prestige?) accents swap /v/ or /f/ for /w/?

Question

I have only a layman's grasp of phonology and a poor ear to boot, but it seems to me that for many Chinese whom I am told have markedly standard pronunciation, /w/ and some type of labiodental fricative are interchangeable. For instance, listen to Echo's 认为 near the end of this episode of Popup Chinese (from about 7:20 onward): http://data.popupchinese.com/778/elementary-it-happened-one-night-traditional.mp3

Am I the only one who hears this? Could these two phonemes be in free variation?

Answer 1

I mentioned this phenomenon in an answer to another post here. This sound, which is actually [ʋ] (labiodental approximant), was also discussed in this post in the Beijing Sounds blog. Being characteristic of the Tianjin region (in my experience anyway), it's not standard, but many people don't seem to notice anyway.

Answer 2

You may find the following references interesting:

1. Hu, Mingyang (胡明扬). 1991. Beijinghua shengmu W de yinzhi (北京话声母W音值) (Phonetic value of W initial in Beijing speech). In: Yuyanxue Lunwen Xuan (语言论文选) (Selected Writings in Linguistics). Beijing: Zhongguo Renmin Daxue Chubanshe. Pp. 244-245.
2. Shen, Jiong (沈炯). 1987. Beijinghua hekouhu ling shengmude yuyin fenqi (北京话合口呼零声母的语音分歧) (Phonetic differences of zero initial before finals beginning with u in the Beijing dialect.) Zhongguo Yuwen (中国语文) 5: 352-36. Transcribed here.