Nokia 2310 Fbus problem

[bmandl]

Hello!
Few days ago, I was trying to establish connection between my nokia 2310 phone and arduino serial via fbus. I used this pinout on nokia and I directly connected nokia phone to arduino tx, rx lines (no level converters). Then I used this program:

/*
 * nokia_serial.cpp
 *
 * Created: 10.2.2013 9:29:01
 *  Author: blaz
 */ 

#include <arduino.h>
byte msg[] = {
0x1E, 0x00, 0x0C, 0xD1, 0x00, 0x07, 0x00, 0x01, 0x00, 0x03, 0x00, 0x01, 0x60, 0x00, 0x72, 0xD5 };

void setup() {
	Serial.begin(115200);
	delay(1000);
}

void loop() {
	// Initialise the F-bus
	for (int z = 0; z < 128; z++) {
		Serial.write(0x55);
	}
	Serial.println("");
	delay(100);
	
	// Send our command
	for (int x = 0; x < (sizeof(msg) / sizeof(byte)); x++) {
		Serial.write(msg[x]);
	}
	Serial.println("");
	
	// Wait for a reply
	while (1) {
		while (Serial.available() > 0) {
			int incomingByte = Serial.read();
			Serial.print(incomingByte, HEX);
			Serial.print(" ");
		}
	}
}

So I can see what's going on. I received nothing from phone. Today, I used two 2.7V zenner diodes as level converters between phone and arduino and when I connect it to arduino, phone first shuts down screen (nothing on, just back light) and then shuts of completely. I can't turn it on until I disconnect it from arduino. What could that mean? Phone worked fine, when I was connecting it directly to arduino and after that, now just after few days, when I was doing nothing, this problem occurs.
Now I noticed, when I use 2.4k resistor in series with arduino tx and phone rx, error goes away, but I still get nothing from phone. And If I use resistor like 330R, error comes back. What does that mean?