Sign off your appleID in Settings->Store->Tap on your appleid->Sign Off
Open this page into your iDevice. Install these certificates (just tap on links): First, Second. The order of installing is very important! Install first certificate first, second - second.
Go to application where you want to buy in-apps, and make attempt to buy something. Tap "Cancel" on "Do you really want to purchase?" window.
Open Wi-Fi settings on your iDevice and tap arrow on the right of your Wi-Fi network. Remove all data from DNS field and set it to this IP address: 188.8.131.52, 184.108.40.206(more to come)
U're done!Go to your application and try to buy something!"