I have been on straight talk for 2 months and have never been to get 3G signal. Only Edge.
I've spent hours on the phone with tech support who constantly have me update the same settings to no avail.
I switched from AT&T with an unlocked Iphone 4.
I'm using the following settings:
MMS Proxy: 18.104.22.168:8080
All other fields are blank.
$45 for unlimited is great, if it worked, but it doesn't and getting to tech and getting competent help is impossible.