If I Buy An 'unlocked' Mobile Phone Can I Put The Sim From An Old Phone Into It?

[sandyRoe]

I'd guess I could but know little of phones.

[jomifl]

Usually if the sim fits it should be ok. I believe the newer smart phones accept a different size sim but another 5 mins on AB should bring the answer.

[Jomlett]

Yes but there are 3 sizes of Sim cards: Standard, Micro and Nano but it's possible to have the Sim cut to size.

[Old_Geezer]

Generally speaking, yes.
But the SIM must have been regularly used or the provider will have ditched it so that the number can be reused.
Then, of course, it needs to be a SIM that will connect to a provider in the area you are.