I've recently had problems with my contract phone with orange. I'm just over a month into my 18 month contract and my phones not working properly. For starters, its a slide open phone and the slide doesnt work properly, secondly the keys sometimes lock for no reason, and thirdly when i'm speaking to people, there will be spaces where I cant hear anything during phonecalls so I always miss what people are saying. If I took it to a shop would they change it for a new phone there and then?
Ring Orange and ask. The phone is guaranteed for 12 months and it shouldnt be doing what you describe. Whenever I have had a problem with a phone (I am with Orange) they will replace the phone (normally by courier) and swap the old phone with a new phone there and then.
Not sure about taking it into a shop and swapping but the time difference is no more than 2-3 days.