First, install the latest version - updated today - overwriting existing (whilst looking at this I noticed a possibly HTML injection vulerability)
Set
Mobile post text to be "UA"
Edit
Mobile Device Post Footer and
Mobile Device Thread Footer plugins and change:
Code:
$vbulletin->options['mo37_post_text'] = $ua_str;
to
Code:
$vbulletin->options['mo37_post_text'] = "Wirelessly posted (" . $ua_str . ")";
or something like that