Martin Scorsese’s “The Departed” just might be the first major movie whose real stars are cell phones. To be sure, the credits give Leonardo DiCaprio, Matt Damon and Jack Nicholson lead billing, but if they focused on ensemble performance, the creatures of Nokia and Verizon would be billed over the title. A movie like “Cellular” has used them in significant supporting roles but modest quantities, and they popped up pretty frequently in “Infernal Affairs,” the Hong Kong movie from which William Monahan adapted this script. But here the devices are numerous and ubiquitous, constantly being pulled out and clasped to famous ears, shouted into, photographed full-face; there are even scenes when one of the little buggers scampers around on a table-top in vibrating mode. Barely five minutes go by before they take center-stage again; the director seems to dote on them the way old Hollywood helmers did the visages of Ingrid Bergman or Greta Garbo.

That doesn’t mean that the movie isn’t enjoyable, because it certainly is, whatever one feels about cells. “The Departed” is different from “Affairs” in quite a few ways–it’s nearly 50% longer, with a much expanded lead female role for Vera Farmiga and more elaborate nefarious schemes and action scenes; it’s transposed to Boston, with all sorts of attendant Irish color; and it contains an added epilogue that either mitigates the cynicism of the original or ratchets it up, depending on your point of view (it’s a far more elaborate addendum than the one found in the international release of “Affairs,” which is included on the DVD) . And, of course, it boasts not only Scorsese’s signature snappy, propulsive style, which easily outclasses the (already solid) direction of the original’s Andrew Lau, and scads of juicy dialogue by Monahan, but also far more footage for the gang boss, a role played by the cool but relatively colorless Eric Tsang in the first movie, but here retooled to give Nicholson the opportunity to go for broke with a portrait of villainy so flashily irresistible that it actually throws his Joker in Burton’s “Batman” movie into the shade. The result is movie as much fun as–though no more profound than–the helmer’s classic Mafia pictures.

“The Departed” is a mirror-image story about two cops, one, Colin Sullivan (Damon)–who looks squeaky clean–a corrupt mole within the force for mob boss Frank Costello (Nicholson) and the other, Billy Costigan (DiCaprio)–from a questionable family background–doing duty undercover as one of Costello’s men for straight-arrow Captain Queenan (Martin Sheen). The convoluted plot has each man trying to uncover the identity of the other; and to enhance the perverse doppelganger nature of their relationship, both of them fall for the same woman, a psychiatrist (Farmiga). It wouldn’t be fair to reveal the neat twists the plot takes as the two men cope with their roles and each simultaneously attempts to unmask the other while protecting himself, but be assured there are plenty of near-confrontations, breathless escapes and surprising quirks. And both DiCaprio and Damon play them with gusto, the former edgy and almost ferret-like, both nervous and cocky, and the latter smoothly aiming to move up the professional ladder but always needing to watch his back.

These two might be the whole show, but here they’re surrounded by a small army of colorful supporting players. The scene-stealing Nicholson, segueing from the morbidly comic to the genuinely threatening with perfect pitch, leads the pack; he’s obviously having a great time with the part, and his pleasure is infectious. It’s a hammy performance, but the ham is tasty. And though Sheen is far more subdued as Costigan’s father figure, he brings authority to the character. Ray Winstone does likewise to the part of Costello’s chief henchman. And there are two other standouts among the cops: Mark Wahlberg, who punches out the hilarious rants of Sergeant Dignam, Queenan’s ultra-loyal right-hand man with hilarious ferocity, and Alec Baldwin, who’s grown into one of the most dependable character actors working today and makes the cynical, floridly loquacious Captain Ellerby a complete joy. The inimitable Kevin Corrigan shows up briefly as Billy’s sleazy cousin, and Anthony Anderson plays it straight as another cop. In fact, it’s only Farmiga who disappoints. She’s perfectly fine, but despite the effort to ramp up her role, this remains a man’s movie in every sense.

On the technical side, this matches the sumptuous quality of Scorsese’s previous pictures. Michael Bellhaus’ widescreen cinematography in superb, filling every requirement in the director’s characteristic bag of tricks, and Kristi Zea’s production design matches it. Equally impressive are Thelma Schoonmaker’s editing, which keeps the story threads clear despite their complexity, and Howard Shore’s moody score. But there doesn’t seem to be a wrangler listed for those pesky cell phones.

“The Departed” isn’t a great movie; like “Infernal Affairs,” it’s efficient rather than profound. But when efficiency is this much fun, it would be churlish to ask for more.