I wanted to post the solution we found for this issue.
First off, after doing some debugging (using an attached Safari Debugger) we found we were receiving two errors:
- 413 - Request Entity Too Large
- The Network Connection Was Lost
We fixed this issue by opting to Ignore Client Certificates in IIS for our application. This is inside the SSL Settings module in IIS.
Logically, I cannot say why this was causing an issue when uploading files over 3G in Safari, but this has resolved our issue.