The entrance to La Fira, Barcelona, the venue of the Mobile World Congress

BARCELONA, Spain –- Europe’s biggest wireless industry trade show starts here on Monday. This year, it’s likely that cellphones will have to share the limelight with a relatively new product category: tablets.

At previous years’ Mobile World Congresses, we have seen the rise of Android, the takeover of multitouch and the push into 3G. But this year the show comes hard on the heels of the International Consumer Electronics Show (which saw the introduction of as many as 80 new tablets) and Google’s announcement of Honeycomb, the tablet-tailored version of its Android operating system.

“There will be a clear discussion on a ton of Android honeycomb tablets,” says Michael Gartenberg, an analyst at Gartner Research, “as well as stuff that will be instantly forgettable.” The challenge, for tablet makers, will be standing out from the crowd.

In other words, expect a lot of gimmicks.

So far, the only officially official Honeycomb tablet is Motorola’s Xoom, but we’re expecting to get some hands-on time with the LG G-Slate, a 7-incher with the dual-core Nvidia Tegra 2 mobile processor, a pair of cameras and — here’s the gimmick — 3-D. The rear-facing camera can capture 3-D and the screen can display it (although you’ll need glasses to see the 3-D effect). The G-Slate will also pack in a 4G radio, making it fully buzzword-compliant.

Also on show will be Honeycomb tablets from Asus. The Eee Pad is likely to exist only behind glass as a prototype, as it is not expected to ship until summer, Asus says.

With any luck, Hewlett-Packard will have the brand-new, webOS-based TouchPad on show, and we’d like to get some hands-on time with the BlackBerry Playbook, and especially to see what it can do when paired with a BlackBerry phone.

More models expected to arrive at the show are the successors to Samsung’s Galaxy S and Tab. A (probably genuine) leaked schedule shows that Samsung plans to introduce the Galaxy S 2 and Tab 2 at a preconference event on Sunday. Rumors say that this may be a 10-inch version of the existing 7-inch Tab, and it is almost certain to run Android 3 Honeycomb.

4G is also likely to be prominent at the show. For the handset makers, its pretty easy: you just make a phone with a different radio, and you can offer your customers faster data download speeds. The problem comes with the carriers, who can’t just switch up things on the production line but instead have to roll out new cell-tower infrastructure. And that takes time.

Expect some news on voice-over-LTE, or VoLTE, the 4G-based internet voice standard that Verizon announced support for recently, says Roger Entner, the founder of Recon Analytics, a market analysis and wireless strategy consulting company.

“The holdup on VoLTE is not device-driven, but network-driven,” says Entner. “We have devices ready to take advantage of it, but the networks are not.”

At first, we’re likely to see a lot of 4G mobile hotspots. These are an easy bet for early adopting nerds, as you get 4G speeds where there is coverage, but we still have a 3G cellphone or tablet to fall back on.

There should be some fun items, too. Sony Ericsson’s Xperia Play, a.k.a. the PlayStation phone, is likely to be ready for some hands-on time. The Android-based phone, shown off in a deeply creepy Superbowl ad this past Sunday, is essentially a Sony Ericsson landscape-slider with a PlayStation game pad in place of the QWERTY keyboard. And that’s really all it needs to be.

The Xperia Play will also be the first handset to get the PlayStation Suite, a software platform and store that will let users of pretty much any modern Android device play Sony’s games.

Finally, 3-D, which showed up strong at CES last year but failed to catch fire in the market in 2010. Nobody bought 3-D TV sets, so it seems that the next battleground will be our cellphones, an even less suitable place for spectacle-encumbered viewing than the TV.

Thankfully, LG will be showing off the LG Optimus 3D, a glasses-free, dual-core-processor packing Android phone. This large (likely 4.3-inch screen) handset is probably little more than a gimmick. It’s possible that its 3-D capabilities will kill battery life, and even if it doesn’t, my guess is that this will be the modern-day equivalent of the analog View-Master. It’ll be fun for a day or two and then the novelty will wear off.

One thing I really hope to see among all of these announcements is some actual prices for tablets. As they pile cameras and other hardware features into slim slate-like bodies, the Motorolas and Samsungs are finding it difficult to match the pricing of the iPad. Moto’s Xoom is pegged at $800 by many rumors, and a 10-inch Galaxy Tab would surely cost more than the already expensive 7-incher. I never thought I’d see the day, but it seems that Apple tablets are likely to remain the cheapest option for some time.