I can fix my iphone using this trick :
1. open kate.app (i know, your touchcreen is dead now)
2. plug your iphone, open itunes, then sync it.
3. wait, wait for about 1 - 2 minute, you will hear sound, then your touchscreen will work again with kate.app open.
4. uncheck everything that you have installed from kate
5. click apply
6. restart the iphone
7. the most important step : uninstall kate !!!!
good luck