You have the following settings for Straight Talk also..
I get about 8 mbps down and 1.5 up.....It's 3g speeds basically...They state they have LTE/4G but I wouldn't hold to that one...I have never seen it yet...This what I would do...I would call and ask them if you're on the att.mvno or the tfdata mvno....If you have the newer sim on the BYOP plan..they tend to push you on the tfdata side...The att.mvno is for the older sims they were selling at get go...Also...check your mcc and mnc and see if it shows 310 for mcc and 410 for mnc...If it shows 260 for mcc that means it's a T-Mobile sim and you'll have to change the mms settings for T-Mobile...
---------- Post added at 09:52 AM ---------- Previous post was at 09:45 AM ----------
You can also go here and put in your number and choose android 4.0/4.1 and it should also tell you what server you should be using...
One thing I will add...I had the same similar problems with the mms on my GT-N7000 and what I did was added the settings and saved and rebooted the phone...It would sit there after rebooted sending pictures...but for some reason it takes the server about 5 minutes to identify your service and settings and finally it'll start pushing them through...
An another thing just came to mind...Under Authentication type set it for PAP and CHAP.And add default,supl,mms under APN type..Now down at the bottom set Bearer to Unspecified then save..If you have it set for LTE it won't work...Been there done that one...