Did they lip-sync Telephone?
 

Someone pointed this out on GGB.
Skip to 1:58, John moves his microphone before he sings his last line but we still hear him singing it.

definately something not quite right there

It'll have been recorded before the show and played back so they could "perform" rather than focus on singing.

they all attended the cheryl cole school of performing 'live'

I swear Cher was meant to sing a line, but didn't.

Of course it was mimed. All the group songs have been. They are on American Idol too.

Who cares? Thats not part of the competition, just a bit of fun. And to expect that many singers to be on cue with their lines? Forget it. If one messed up(hi Wagner) it could throw the whole performance into chaos.

So, trust me, its best they mime.

all these from last year too have been mimed no?

Yeah deffo mimed, how amazing is Rebecca's voice here though :O

They sing and they play a recorded track over just in case. Getting sound from someones voice down into your telly speakers is not as easy as it seems.

All the group songs are mimed - same as American Idol. They are not judged on the group song and it's just a bit of group fun.

Who doesn't like a bit of group fun! I know I do!

Yes, she did, at 1:23.

I thought Cher looked great in the group song. She just burst out of nowhere and actually looked like the star.

Yeah yeah, I know some will disagree but thats my honest opinion.

Also, you should realise that they really don't have much time to all get together and rehearse these group songs so its enough they learn the choreography let alone learn to sing on cue live. I think they do well considering. Enjoyed all of them so far.

Yes, all group performances have been mimed

They always mime the group performances

You know those group performances? All mimed.

Paije is the biggest giveaway

what the last 3 posts said.

i'm more concerned by One Direction's help in their performances.

I hate how they slowed the song down :/