So the Google-Microsoft rivalry entered a fascinating new phase, with Google launching a software stack for the fastest-growing category of computers in the coming decade -- the tiny ones that fit in your pocket.

Phone companies now have a great negotiating tool when dealing the established mobile operating system vendors, and Microsoft has a fire lit under it to accelerate work on its ultra-mobile PC platform.

Widget developers are probably thrilled -- because no doubt there will be an easy way to develop their applications for both Google's OpenSocial platform and Google's Open Handset platform -- although hard-core device and application developers are probably also fired up by the Sync software stack that Microsoft is talking up today in Barcelona.

But so far there's not much to get consumers excited. In fact some may be less than excited at the prospect of Google-powered phones. It will be quite a test of the cuddly, do-no-evil brand.

A few questions:

Just how open will this stack be? Is the Google mobile ad placement system an optional component? How about the end user agreement? Will a contract with Google, authorizing its ad delivery, be mandatory for everyone using or developing phones with this software?

Will consumers be excited about mobile phones developed by an enormous advertising company like Google?

The cost savings of Google's software won't matter to most phone buyers. They already expect mobile phones to be free or nearly free.

What people don't like, though, is the intrusion of advertising via telephones.

In fact they hate ads on their phones so much, the country has regulations against uninvited solicitations and federal services such as the do-not-call registry.

Telemarketers are prohibited from automatically pitching your phone. There are also some regulations against unwanted text messages from solicitors.

How does the spirit of those regulations jive with Google's plans for targeted advertising on mobile phones? Do people want geographically precise ads synced to the activities they're doing on their mobile phone?

That gets back to my question about the openness of the Google software stack. The user agreement will no doubt say that by using the software, you're authorizing the company to deliver ads to your phone.

Unless the software is truly dazzling and the cost savings really significant, that may really limit its appeal.

But maybe I've got it wrong and mobile ads are just inevitable. Phone companies are obviously thrilled by the prospects of Google-style advertising.

Resentment of advertising via phones may be a generational thing; the FCC's do-not-call regulations seem to appease mostly older people who particularly resent being harangued via the phone service they're supporting with a monthly rate.

Perhaps future generations of phone users won't care as much, although I still think most people consider the phone to be a personal device for private communication. This may change as we move from phones to mobile computing devices, but ads, especially targeted ones, diminish the sense of privacy.

Meanwhile, it will be interesting to see if and how the FCC regulations adopt to phone ad delivery platforms such as the one Google rolled out today.

Until there's some kind of "opt-out" option for mobile device ads (don't hold your breath ... ) the onus will be on consumers to sort through the phone options and contracts and decide whether the convenience of Web applications on their phone is worth the privacy tradeoff.