Here is the list of MMS and APN Settings for the major carriers in the US, including prepaid data services. They are important to be setup properly so that your mobile phone can connect properly and be able to use the mobile data plan you are subscribed to.
APN Settings for T-Mobile
AT&T APN Settings
Correct APN Settings for Straight Talk
Should you have any issue with the above settings, please leave us a comment and we will get back to you