Here is the correct APN Setting for Straight talk users!
This will give you mms and internet!

First download Apn Backup and Restore app from app store, and delete all existing APNs. Then manually enter APNs. In android you must have 2 apns setup for mms to work (at least in my case).

Here are my settings:

Name
HOME

APN
att.mvno

Leave everything else alone EXCEPT the bottom selection that says:

APN type (here you must enter the following)
default,supl

Then save, next choose to add another APN
make it look like this:

Name
MMS

APN
att.mvno

skip down to
MMSC
http://mmsc.cingular.com

MMS proxy
proxy.mvno.tracfone.com

MMS port
80

skip to:
APN type (enter the following)
mms
THEN SAVE

You will see that only one APN has the option to be chosen, that is ok, Just choose the one that is able to be chosen.

Now go back to Homescreen and then reboot your phone.
This works for me, hope it can help you. I tried a hundred different ways and this was it. Capitalisation is important, and the APN type was the trick.
GOOD LUCK and let me know if it worked for you.

Note:
With this setting once in a while 3G will cut in and out, but other than that Ive been running these settings on my device and it works pretty well.

Reference:
Does anyone know the proper APN settings for Android Devices?