arduino and Sony ericsson t230 problem

Hello, i have a strange problem with interfacing with ericsson t230. All my code is working properly for some time (few minutes) and then phone stops responding to any queries. When restarting arduino everything is working. I can make a call, receive and send messages but after this few moments i'm not able to do anything what involves gsm modem from ericsson. if i put something else to the code - rest is working but not the communication with gsm modem. I'm using hardware serial of the arduino instead of software serial because my arduino is on a breadboard so hardware serial is free to use. I cannot use software serial because it interfere with my nrf24l01+ library. All code that i'm using is made of few other codes found on the internet. i believe that the phone is going to sleep or some other state because when i send sms to the ericsson nothing happens but message is in the phone storage not deleted at it should be while executing the code. How to prevent that? What can be a problem? why it isn't responding after a while? What to do

sorry form my english :)

This topic can be closed. Problem solved by changing phone. This one was damaged somehow.