Wowza. H2O has a lot of configurations out there.
Here's from H2O's own website:
However - cruising around the net I see a mix of att.mvno or prodata for the APN. It also looks like the MMSC URL you are using matches the att.mvno APN and not the prodata. Prodata APN takes a MMSC URL of
http://mmsc.mobile.att.net so there is a mismatch right there.
Here are a couple of more recent success stories from How@^* forums:
H2O Wireless APN Settings - Page 2
Based on H2O preferring att.mvno config, the above forum posts and other stuff I looked at...
I recommend you change your APN to att.mvno and for MMS change to these settings by unlockit.co.nz who are usually spot on in my experience. (
Mobile Phone Carrier Settings for H2O Wireless - United States)
If the above does not work - change ONLY the WAP gateway (URL) from the "proxy text string" to 66.209.11.33
or
then also change to max size 10000.