user4982: Do I have to connect RX and TX of SIM900A with any pins (say TX, RX of Arduino) for network purpose? Shouldn't the network status LED blink slower after connecting the power sources with SIM900A?   

user6936: To answer your questions in turn:

It is not necessary to connect to the Arduino solely for the purpose of making a GSM network connection. 
When the SIM900A is powered on, the Status LED will blink once every second.
When the GSM connection has been established the Status LED of the SIM900A will blink every 3 seconds.

Follow this guide, from Tutorial to interface GSM SIM900A with Arduino:

Initial startup of SIM900

Insert your SIM card to GSM module and lock it.
Power up the SIM900A by connecting it to Arduino's 5V and GND pins
Connect the Antenna 
Now wait for some time (say 1 minute) and make note of the blinking rate of ‘status LED’ or ‘network LED’ (D6). 
  The GSM module will take some time to establish connection with mobile network
Once the connection is established successfully, the status/network LED will blink continuously every 3 seconds. You may try making a call to the mobile number of the sim card inside GSM
  module. If you hear a ring back, the GSM module has successfully
  established network connection.

Connection to Arduino
The SIM900A has the following pins:

3VR; 
3VT; 
5VR; 
5VT; 
VCC, and; 
GND.

For serial communication between the Arduino and SIM900A module. you
  have to connect:

SIM900A 5VT to Arduino D9 and;
SIM900A 5VR to Arduino D10

Basic Communication

To change SMS sending mode: AT+CMGF=1
mySerial.println("AT+CMGF=1");

To read SMS in text mode: AT+CNMI=2,2,0,0,0
mySerial.println("AT+CNMI=2,2,0,0,0");

To make a call: ATD+60XXXXXXXXX (replace X with number you want to call, change +60 to your country code)
mySerial.println("ATD+60XXXXXXXXX;"); 

To disconnect/hangup call: ATH
mySerial.println("ATH");

To redial: ATDL
mySerial.println("ATDL");

To receive a phone call: ATA
mySerial.println("ATA");




4982: <p>Do I have to connect RX and TX of SIM900A with any pins (say TX, RX of Arduino) for network purpose? Shouldn't the network status LED blink slower after connecting the power sources with SIM900A?   </p>
 6936: <p>To answer your questions in turn:</p>

<ul>
<li><p>It is not necessary to connect to the Arduino solely for the purpose of making a GSM network connection. </p></li>
<li><p>When the SIM900A is powered on, the Status LED will blink once every second.</p></li>
<li><p>When the GSM connection has been established the Status LED of the SIM900A will blink every 3 seconds.</p></li>
</ul>

<p>Follow this guide, from <a href="http://www.instructables.com/id/GSM-SIM900A-With-Arduino/" rel="nofollow noreferrer">Tutorial to interface GSM SIM900A with Arduino</a>:</p>

<blockquote>
  <h3>Initial startup of SIM900</h3>
  
  <ol>
  <li>Insert your SIM card to GSM module and lock it.</li>
  <li>Power up the SIM900A by connecting it to Arduino's 5V and GND pins</li>
  <li>Connect the Antenna </li>
  <li>Now wait for some time (say 1 minute) and make note of the blinking rate of ‘status LED’ or ‘network LED’ (D6). 
  The GSM module will take some time to establish connection with mobile network</li>
  <li>Once the connection is established successfully, the <em>status/network LED will blink continuously every 3 seconds</em>. You may try making a call to the mobile number of the sim card inside GSM
  module. If you hear a ring back, the GSM module has successfully
  established network connection.</li>
  </ol>
  
  <h3>Connection to Arduino</h3>
  
  <p>The SIM900A has the following pins:</p>
  
  <ul>
  <li><code>3VR</code>; </li>
  <li><code>3VT</code>; </li>
  <li><code>5VR</code>; </li>
  <li><code>5VT</code>; </li>
  <li><code>VCC</code>, and; </li>
  <li><code>GND</code>.</li>
  </ul>
  
  <p>For serial communication between the Arduino and SIM900A module. you
  have to connect:</p>
  
  <ul>
  <li>SIM900A <code>5VT</code> to Arduino <code>D9</code> and;</li>
  <li>SIM900A <code>5VR</code> to Arduino <code>D10</code></li>
  </ul>
  
  <h3>Basic Communication</h3>
  
  <ol>
  <li><p>To change SMS sending mode: <code>AT+CMGF=1</code></p>

<pre><code>mySerial.println("AT+CMGF=1");
</code></pre></li>
  <li><p>To read SMS in text mode: <code>AT+CNMI=2,2,0,0,0</code></p>

<pre><code>mySerial.println("AT+CNMI=2,2,0,0,0");
</code></pre></li>
  <li><p>To make a call: <code>ATD+60XXXXXXXXX</code> (replace X with number you want to call, change +60 to your country code)</p>

<pre><code>mySerial.println("ATD+60XXXXXXXXX;"); 
</code></pre></li>
  <li><p>To disconnect/hangup call: <code>ATH</code></p>

<pre><code>mySerial.println("ATH");
</code></pre></li>
  <li><p>To redial: <code>ATDL</code></p>

<pre><code>mySerial.println("ATDL");
</code></pre></li>
  <li><p>To receive a phone call: <code>ATA</code></p>

<pre><code>mySerial.println("ATA");
</code></pre></li>
  </ol>
</blockquote>
