How do you buy a ringtone for the tentative Iphone?

I just bought the I-phone 3G and I don't know how to buy a ringtone. Help?

---

Answers:    itunes..

or go to Ventones'.com'
to acquire them for free

works on iphones
they send the ringtone toy our phone

---

Why does my AT&T sim card not work beside my apple iphone 3g 16g (bought from ebay)?

What happen to the iPint app. on the App. store for the ipod touch/iphone?

Can you do these next to the iPhone 3G?

Questions concerning iPhone 3G?

How do you unlock password for iphone if forgotten?