Change the number of home screen panels in Android A phone user manual (HTC Wildfire S. Android 2.2) says 


  'Home screen has seven panels that you can customise'.


The system settings do not contain an option to modify the number of panels.

I was searching for this on the web and was not able to find any solution that does not involve third-party applications.

If this requires programming, please, move the question to StackOverflow and respond with detail.
If you don't want use 3rd party apps:

This requires decent computer skills and a rooted phone, but here are the steps for android 2.3 Gingerbread.


Copy /system/home.apk from your phone to pc.
Decompile home.apk using apktool.
Goto [decompiled folder]/res/values/integer.xml    
Change &lt;integer name="number_of_desktop_panes"&gt;5&lt;/integer&gt;, to 7 or whatever you want.
Save it,and compile the apk using apktool.   
Copy it back to phone i.e to /system,change its permissions to -rw-r-r.