new bool:Window[MAX_PLAYERS];
public OnPlayerText(playerid, text[])
{
    if(Window[playerid])//means open
    {
        new string[128];
        new pName[24];
        GetPlayerName(playerid, pName, sizeof(pName));
        format(string,sizeof(string),"%s says: %s",);
        CloseMessage(playerid, -1, string);
    } 
    else if(!Window[playerid])
    {
        //do nothing
        printf("%s Window's is closed no one can hear him!",pName);
    }
    return 0;
}

//Set this to your car window command 
//if open Window[playerid] =true; 
//if close Window[playerid] =false;

stock CloseMessage(playerid, colour, string[])//thanks iGetty for this function
{
    new Float: PlayerX, Float: PlayerY, Float: PlayerZ;
    for(new i = 0; i < MAX_PLAYERS; i++)
    {
        if(IsPlayerConnected(i))
        {
            GetPlayerPos(playerid, PlayerX, PlayerY, PlayerZ);
            if(IsPlayerInRangeOfPoint(i, 10, PlayerX, PlayerY, PlayerZ))
            {
                SendClientMessage(i, colour, string);
            }
        }
    }
    return 1;
}