In what will certainly be viewed as an escalation of the Google vs. Apple tensions, a new report finds Cupertino in talks with once bitter rival Microsoft to make their Bing service the default search engine on the iPhone.

AppleInsider is reporting on the rumored discussions, which have reportedly been going on “for weeks” according to BusinessWeek and two sources said to be familiar with the negotiations. Presumably, such a coup would also make Bing a search option within Mobile Safari, which currently has only Google and Yahoo.

“Apple and Google know the other is their primary enemy,” a source relayed to BusinessWeek. “Microsoft is now a pawn in that battle.”

Apple and Google have seen tensions between them escalate in recent months, culminating in Google CEO Eric Schmidt resigning from the Apple board of directors last summer as the U.S. Federal Trade Commission launched an investigation into the connections between the two companies.

The two tech giants continue to encroach on each other’s turf, with Google’s Android now hotly competing for mobile space with Apple’s iPhone, both companies buying up mobile ad firms, Google’s forthcoming Chrome OS coming to the desktop to compete with the likes of Mac OS X and their Chrome web browser already putting Apple’s Safari in the crosshairs.

Of course, it’s no secret that Microsoft themselves have it out for Google, and the Bing search engine unveiled last year was most definitely a shot across the bow of the Mountain View, California search giant.