You download whatever format you want of the ringtone and then you add it as an attachment to your email. Then you address the email, for example, to 1234567890@vzwpix.com for verizon or if you have another carrier you can probably figure out the @whatever by going to their website or googling it.
I would suggest going with blue tooth, SD cards, or USB to phone cables to send them to your phone. It's really your best best, as email is 100% reliable.