1 - Is your APN set correctly.
2 - You do know mms need your data on to send and receive mms, it will not send or receive thru wifi.

Name: MediaNet mms
APN: wap.cingular.com
Proxy: blank
Port: 80
Username: WAP@CINGULAR.COM
Password: CINGULAR1
Server: leave blank
MMSC: http: //mmsc.cingular.com
MMS Proxy: wireless.cingular.com
MMS port: 80
*MMS protocol: WAP 2.0 (if there is an MMS protocol spot)
MICC 310
MNC 410
Auth type: blank
APN type: default,supl,mms
APN protocol: IPv4
Bearer: unspecified
PHONE: AT&T Samsung Galaxy S4 (MDL)
ROM: Goldeneye V34
Baseband : NC1