Try this out. All credit goes to JKing106.
I have just edited things for brevity.
Ensure that all fields under the "Cellular" entry are blank.
Create a "Straight Talk" entry using Nokia's Access Point app.
If you don't have Access Point app or do not find it in the App Store, look for an App called Sysapp Pusher in the App Store.
After installing Sysapp Pusher, install "Extras + Info" from Sysapp Pusher. Access point should now be visible in your Settings menu.
Now create Internet APN and MMS settings as shown below:
Internet APN info for Access Point:
Access Point Name - straight talk
Username - blank
Password - blank
Proxy Address - mms3.tracfone.com
Proxy Port - 80
Network Type - IPv4
Authentication Type - none
MMS Settings
APN - tfdata
User- blank
Pass - blank
Proxy address - 66.209.11.33
Proxy port - 80
MMSC address -
http://mms-tf.net
Network - IPv4
Authentication - none