What APN Setting Ultimately Works for AT&T HTC One using Straight Talk BYOP SIM Card

[VerizonSalesRep]

Agh, tis sweet not to have to worry about high carrier prices thanks to Straight Talk BYOP. However, it's been a headache getting the right APN setting on the phone that can assure expedient receiving or sending of MMS. Just wondering if there's anyone that knows the best setup for the HTC One. I even downloaded Straight Talk's Data Application Settings app from the Google Play Store, but MMS is still Xmas slow. Any help would be greatly appreciated!