That's the question on everyone's lips in the mobile industry right now. Cue scratching of heads, shuffling feet looking at the floor and mumbling "errr... LTE, probably."
But my prediction for this year's event, which is almost among us, is that EVERYONE will be talking about applications. Or, more specifically, applications stores, akin to Apple's famous App Store.
I've heard along the grapevine that a number of different players, from all corners of the telecoms world, are planning to use MWC 2009 to unveil their own versions of the hugely successful App Store.
Watch this space... Or better still, monitor developments at the show by logging onto to Total Telecom - that's http://www.totaltele.com/ - from Monday, when our dedicated Mobile World Congress news service goes live.