Issue in GSM for Straight Talk and MMS.
Try with these settings: http://apn.gishan.net/settings/os_12_11_android_4.4kitkat_internet_and_mms_settings_for_straight_talk.php

Should work. Sorry. Site does not allow me to copy the settings. 
How ever if you cannot receive MMS that should be a data problem. Please check you can access data properly. MMS APN is only for sending MMS. Do you receive MMS notification at least?