Okay, so this issue was bugging me to no end.  After tinkering with the filesystem myself I came across a post in the Apple Discussion Boards which confirmed my findings.  There is a bug in Safari on the iPhone…well not really a bug, it’s a permissions issue.  The Cookies directory does is not writable by the default “mobile” user.

Here’s a quick fix if you don’t want to scroll through the link above:

  1. SSH into your iPhone as the root user.
  2. Type the following commands:
    • chown mobile /var/mobile/Library/Cookies/
    • chown mobile /var/mobile/Library/Cookies/Cookies.plist
That’s it.  Safari should now be able to retain your login details.