Here's what's working best for me. I have a Verizon Motorola Droid Mini that I'm using on H2O. I'm disappointed that I don't get true 4g speeds, stuck on H+ but these settings have clocked download speeds over 7mbps. Also, picture messages work. Always striving to get better so if you improve on these, please share.
Name: H2O
APN: att.mvno
Proxy: Not Set
Port: Not Set
User Name: Not Set
Password: Not Set
Server: Not Set
MMSC: h ttp://mmsc.cingular.com (can't post links)
MMSC Proxy: proxy.mvno.H2OMobileweb.com
Port: 80
MCC:310
MNC:410
Authentication Type: CHAP
APN Type: default,supl,mms,hipri
APN Protocol: IPv4/IPv6
APN Roaming Protocol: IPv4
Bearer: Unspecified
MVNO Type: None

Hope this helps!