To help divine the meaning of today’s big Microsoft-Yahoo (NSDQ: YHOO) announcement, RBC analyst Jordan Rohan just hosted a call for clients. Some highlights, per my eavesdropping:

-- Why now?: Yahoo is obviously in a weak position, as its share price is only moving downward. It’s not clear exactly how things went down at Yahoo, with last night’s resignation of Terry Semel from the company’s board, but, as Rohan put it, it’s “Obviously not a total coincidence.” His departure represents “one less vote that would have to be swayed.” Also, it’s dawning on Microsoft (NSDQ: MSFT) that technology alone won’t win the day online. It needs scale to be an effective player in online ads. This is what it’s all about: scale, scale, ads, ads, and more scale.

-- Regulatory issues: RBC’s Fred Boucher predicted a ”lengthy regulatory review,” citing Google-DoubleClick as a point of reference. But ultimately he expects the deal to gain approval, because regulators will like to see the emergence of a strong number two in this Google-dominated market. But: “Microsoft is going to go in front of the regulators with Yahoo on their side.” In other words, the regulatory hurdle will be much higher if Yahoo’s board doesn’t give the thumbs up and the offer turns completely hostile. So there’s a chance that the deal price might be bumped slightly, as a sweetener to get support from Yahoo’s board.

-- Bidding war?: Unlikely. Rohan predicted that there are discussions going on at GE, Comcast (NSDQ: CMCSA) and News Corp (NYSE: NWS). right now about whether to get involved… ”The discussion is very brief… Microsoft is the one company in the space that could easily up their bid to levels that could drive anyone else out.”

-- Google: Rohan: “Google (NSDQ: GOOG) has taken Microsoft’s place as the big, bad tech bully.” Google will benefit, from a regulatory perspective, by having a more serious competitor.

-- One less buyer: The losers could be the medium-sized online player that will have one fewer cost-insensitive bidder. Both Yahoo and Microsoft have paid premium multiples for deals in the last year or so: aQuantive, Right Media, Blue Lithium, etc. Arguably, as Rohan noted, competition between the two companies played a role in inflating these premiums. Assuming the deal goes through, this means less competition for certain deals