MakeItMine is a free iphone app on cydia which allows you to set custom text on iphone status bar in place of Carrier name and banner.
In order to locate the app, Open Cydia on your iphone and search for the text MakeItMine
Install this app on your iphone, by tapping the Install button after finding the application
Run this application and type the custom name in the text box shown in the application, tap the carrier button to set the text in place of the carrier name and banner button to set the text in the middle of the status bar.
Note: You can set different text for carrier name and middle text banner.
PS: If you have any problem in using this simple application, let us know by leaving your comments at the end of this post.