How to make "IF "Temperature exceeds" logic to work in same arduino code

The code below will check if the temperature goes above 29 degrees. It also check whether the temperature was below 29 previously, to prevent it from sending an SMS every second, for as long as it's above 29 degrees C.

#include "SIM900.h"
#include <SoftwareSerial.h>
#include "call.h"
#include <DHT.h>
#include "sms.h"

SMSGSM sms;
#define DHTPIN 7  
#define DHTTYPE DHT22   

CallGSM call;
boolean started=false;
char sms_text[160];

DHT dht(DHTPIN, DHTTYPE);

void setup()
{
    dht.begin();
    Serial.begin(9600);

    if (gsm.begin(9600)) 
    {
        Serial.println("\nstatus=READY");
        started=true;
    } 
    else 
        Serial.println("\nstatus=IDLE");
}

float previousTemperature = 0;
void loop()
{
    float humidity, temperature;
    humidity = dht.readHumidity();
    temperature = dht.readTemperature();
    delay(1000);

    // check if temperature has raised to above 29 degrees
    if(temperature>29 && previousTemperature<=29)
    {
        sendSMS(temperature, humidity);
    }
    previousTemperature = temperature;

    // check for incomming call
    switch (call.CallStatus())
    {
        case CALL_NONE: // Nothing is happening
            break;

        case CALL_INCOM_VOICE : // Yes! Someone is calling us
            Serial.println("RECEIVING CALL");
            call.HangUp();
            delay(1000);
            sendSMS(temperature, humidity);
            break;

        case CALL_COMM_LINE_BUSY:  // In this case the call would be established
            Serial.println("TALKING. Line busy.");
            break;
    }

    delay(1000);
}

void sendSMS(float temperature, float humidity)
{
    String smsText ="";
    smsText = "Temperature: "+String(temperature,1)+"C Humidity: "+String(humidity,1)+"%";
    smsText.toCharArray(sms_text,160);
    //Serial.println(smsText);
    sms.SendSMS("+91**********",sms_text);  
}