I got an iPhone. And I logged into my iTunes on my phone and?

And I wanna redownload all my music from my iTunes from when I had an iPod. Will it cost data? I have 750 songs on there and that would use all my data.

It will use a lot of your space. I had all my songs on my iPhone, and I took all but 100 off. I just use my iPod for songs, and I listen to iTunes radio more than my actual songs. Your songs won't use data, just the space on your phone.