GigaOm reports that Amp'ed has filed BK. It owes over $100M with just 200k subs. Amp'd has received $350M in funding. ($450M for 200,000 users = $2250 per user). Fierce states some numbers here. (ARPU of $100 due to downloads and media, which explains all the creditors).
Update: apparently, Amp'ed couldn't even make a $4.5M payment to VZW, who then canceled their wholesale agreement [source]
Amp'd Flickr ad here.
The reasons cited here for the BK are (from Amp'ed) grew too fast; (from analyst) too costly for handsets and marketing.