Hi. You can get an iphone from various outlets but at the moment only on o2 as they have the exclusive rights. That is all set to change shortly however.
Your daughter will need a computer of some sorts as it needs to be activated initially through itunes on your computer. In addition backups of the iphone are performed through itunes on your pc. If your daughter wants to put music on the ipod part of the iphone again it is done through itunes etc etc. So yes, I would say a computer is essential to owning an iphone.
The iphone is good or even very good except for the the rubbish bluetooth support, I can go into further details if you are interested.