orange monthly contract sim card

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Does anybody know if a sim card from a phone on a monthly contract with orange will work in an unlocked jam - I really don't want to have to change my number. In addition this sim card has two lines on it - will that work too on the Jam/MDA?

Hope someone can help as this would put me over the edge on a buying decision

I would have thought this would work. How did you get on in the end?