ListActivity or listview problem in android

I made one ListActivity and i install开发者_JAVA技巧ed in samsung galaxy phone and htc wildfire. But in list some lines between two rows are not visible. what is the problem? Is there problem in my code or in phone ? I have same problem with sipdroid application available in android market. Is there any idea ?

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Is there problem in my code or in phone ?

Android is probably scaling your UI. Make sure you have the appropriate <supports-screens> element in your manifest to declare what screen sizes your UI code handles directly.