Let the invasion of the cupcake trucks begin.

True, Flirty Cupcakes has merrily been doing its cupcakes-on-wheels thing for a few months now.

But with Monday's opening of Sprinkles Cupcakes at 50 E. Walton -- the first Midwest outpost of the Los Angeles-based cupcake chain -- the roads are about to get crowded.

The Sprinklesmobile will be "cruising around the city for the next few weeks giving away free cupcakes," says spokeswoman Jill Katz. Chicagoan-gone-Hollywood Bill Rancic and wife/E! News host Giuliana Rancic will add star power/enviable tans to opening day by working the counter from 11 a.m. to 1 p.m. and autographing cupcake boxes, Katz says.

Not to be outdone, more, the cupcake boutique at 1 E. Delaware -- just a stone's throw from Sprinkles -- is launching its More Mobile and in its first week, also will be giving away the handheld treats for free.

More owner Patty Rothman hopes to roll out the truck by a week from Friday -- which, not coincidentally, is opening day of the Lollapalooza music fest in Grant Park. The cupcake shop is one of the high-profile vendors in the fest's new and culinarily improved Chow Town food area.

"The best thing I can do is to try and associate myself with being from Chicago," Rothman says.

One sign of a city girl: Rothman's done her homework. In anticipation of a future overhaul of the city's ordinance pertaining to mobile food vendors, and as a nod to the environmentally conscious Mayor Daley, she outfitted her truck with a generator that keeps it refrigerated and air-conditioned even with the motor off. The truck will hold an imposing 1,500 cupcakes in 12 flavors.

As for the competition, Rothman offers this diplomatic take: "At the end of the day, there's enough room for everyone... Truly, I'm always fascinated by how excited people get over cupcakes."

Mm, hmm -- whoops, I mean, mmm.

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