Default Net10 throws me another APN curve

I have 2 Galaxy S3's activated on Net10--mine is a GT-i9300 and my wife's is a SGH-i747. My mobile data performance has been intermittent since joining early last month. Their phone support has been provisioning me with the "att.mnvo" APN settings while my wife's phone got the "tfdata" set. Hers won't work on mine and mine wont work on hers. I've asked repeatedly here for help understanding why this is so but haven't gotten any help.

Monday afternoon my mobile data quit again so I made another call to Net10 when I got home (so far I've been on the phone with them 197 minutes in 6 weeks). THIS time they gave me the "tfdata" settings. It worked--even though I had tried that set as recently as Friday. THIS tech THIS time told me these settings will NOW be permanent. I'm doubting.

IF anybody understands how this works PLEASE clue me in why it works like this.