ok my question is.. i know att will somehow make me take the 30$ data plan but for now i cancell that and using the 15$ plan. Will my data usage be charge more per bytes or the same unless i go over the 5g cap? also i cant setup my voicemail, it keeps asking for my mailbox number which i thouggt was my phone number but its not working. i hold #1 to get to my voicemail but cant set up. btw my phone is not jailbroken cuz i drop my phone and mess up the screen so i did an upgrade and brought to apple for repair.

You should have unlimited data with that $15 plan. I used to have the same plan before I left AT&T. Just be careful not to drop that plan because AT&T does not offer it any longer. If you are to activate a new phone with AT&T it must be the $30 plan, no matter what kind of smart phone you have.