Mediapost reports on Google's appearance at the Television Bureau of Advertising's annual marketing conference. So far, advertisers interested in Google's foray into TV ad brokering have been able to participate only if invited. But a top company executive said Thursday that could change "very soon." When it does, Google's platform will presumably allow marketers to log into a Google-managed interface and place a buy for a national cable spot without much gate-keeping. The "invitation-only" test phase for Google TV Ads--where vetted advertisers purchase inventory on networks offered by Dish Network--would then morph into what Google refers to as "general availability."