iPhone 4s not connecting to the Internet using the sim and heating up in standby
The next things to replaced once you've replaced the antenna and the battery are to double check the wires and connection points and then replace the logic board which contains both the cellular chip and the firmware/software to run that part of the system.

Field test mode might also let you know what signal levels are being reported/measured and compare them with other iPhone 4S if you have them handy.


iPhone 4 has 3G connectivity but can&#39;t access internet
iPhone field test instructions