Sending SMS message vis GPRS SIM900A with Arduino UNO is not reliable

[J-M-L]

we miss information on what printSerial() is

@seccpur

		while (!printSerial("OK"))
		{
			delay(1000UL);
			if (millis() - start_time > 20000UL) {
				time_out = true;
				break;
			}
		}

may be the timeout is too short? may be using delay() for 1s is a bad idea and you flood the incoming buffer and loose the OK (if there is a lot of chatter happening during that second)