I can't download songs from Itunes with Iphone 5

Hi,

Just a quick and probably easy to answer question (im a bit slow with the apple thing)

when i log into Itunes from my Iphone 5, ALOT of the songs are greyed out & i can't download them...

Very few songs ARE available, but not many...

I've checked restrictions, backed up & restored through Itunes & downloaded the latest update...

anyone able to help me?!

thanks

Karena