Easiest way is to modify the file bottombarlocktextmask.png using a graphics editor like photoshop or PSP. I use theis as part of my Winterboard theme and the modified file is placed into: /private/var/stash/Themes.H3ollG/your theme name/Bundles/com.apple.TelephonyUI
the text printed in red will be different for each user.
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iPhone, the Swiss Army knife of the 21st Century.