Here are some more details on the game:
http://arstechnica.com/news.ars/post/20080121-ea-revamps-battlefield-with-free-ad-supported-online-title.htmlSome of the more important bits from it are:
>> "[Ads] wouldn't work inside the fictional world. Instead, adverts will appear on the website and the 'front-end' of the game," Ben Cousins, the senior producer at DICE
>> The for-pay items will also only make cosmetic changes to your character; nothing you buy in the game will give you an advantage in actual game play. For example, you may pay a dollar for a new rakish hat, but you won't be able to pay for a gun that shoots faster or does more damage.
EDIT: So, I'm assuming based on this, that you WON'T be able to pay for any advantages (like skills or weapons), just cosmetic touches. I imagine this would spill over to buying additional levels/boards as per the BF2 "Booster Packs."