What are all those Vonage ads doing in Yahoo! Mail?

VoIP marketing, like politics, makes strange bedfellows.

I'm not the only one that sees Yahoo Messenger's expanding voice services as a competitive threat to Internet phone specialists such as Vonage.

Yet according to Internet marketing and advertising news publisher MediaPost, Vonage is a prominent advertiser on Yahoo! Mail. 

In relation to survey firm Nielsen/NetRatings estimates that online ads were served up on the Web 123.6 billion times in December, MediaPost's Wendy Davis writes: 

Yahoo Mail accounted for 21.7 percent of impressions - up from November's 16.7 percent, thanks in part to a significant increase in advertising by Vonage Holdings. MSN Hotmail garnered 7.5 percent, down from November's 7.9 percent. MySpace served up 4.8 percent of ads; its year-high share of impressions was 12.4 percent, in September.

So why are these two inevitable competitors doing business together?

Well, maybe it has to do with Vonage having deep ad pockets and spending the money where they feel they can get the eyeballs. And Yahoo! not caring where they get their ad revenue, even if it is from a company who is starting to compete against it, and will do so even more in the future.

I guess this dance of expediency is one example of what marketers call "co-opetition."