it might be different from carrier to carrier, but this is exactly what i did:
A: Make the ringtone in whichever way you chose, or find one. whatever the case, get the ringtone part finished.
B: Download it as an MP3 (or perhaps one of the other formats) to your PC. I downloaded mine as an MP3 and had it saved and used windows media player to open it.
C: I sent it as an email attatchment using my current hotmail account to my cellphone number as a text. I assume your phone NEEDS to be COMPATABLE with receiving texts and/or downloads [I.E. no dinosaur phones]
all cellphones that are new enough and have text messaging can receive emails as text messages. you dont have to go online and check your email with your phone, you just text it. so if your phone number was hosted by verizon it would look like this: (555)555-5555 right?