user40208: I am using SIM800L module. I am new to GSM modules. I have searched in many web sites about SIM800L, every where they mentioned baud rate 9600 for SoftwareSerial but it is not working at all in my case. So I started a trail and error method to match baud rate. Finally I found that its baud rate is 38400. With baud rate of 9600 for Arduino and 38400 I am able to communicate with SIM800L.
The problem is that I am unable to register to network. AT+COPS=? shows all available networks. Using AT+COPS="value" I am able to select network. But after that the SIM800L module still blinks every second.
In loop() I am continuously reading software serial and it's printing the following: 
RDY
+CFUN: 1
+CPIN: READY
Call Ready
SMS Ready
RDY
+CFUN: 1
+CPIN: READY
Call Ready
SMS Ready

The above data is continuously printing on console.

user43604: I am 90% sure it's a power issue. Not sure on what board/module you're using but the SIM800L/SIM900 needs a burst of current of 2 A during 577 µS (See the manual). 
Try using 4700 µF and a 10 µF capacitor in parallel with the module. Powering it with a proper power source instead of the Arduino wouldn't hurt too.

40208: <p>I am using SIM800L module. I am new to GSM modules. I have searched in many web sites about SIM800L, every where they mentioned baud rate 9600 for <code>SoftwareSerial</code> but it is not working at all in my case. So I started a trail and error method to match baud rate. Finally I found that its baud rate is 38400. With baud rate of 9600 for Arduino and 38400 I am able to communicate with SIM800L.</p>

<p>The problem is that I am unable to register to network. <code>AT+COPS=?</code> shows all available networks. Using <code>AT+COPS="value"</code> I am able to select network. But after that the SIM800L module still blinks every second.</p>

<p>In <code>loop()</code> I am continuously reading software serial and it's printing the following: </p>

<pre><code>RDY
+CFUN: 1
+CPIN: READY
Call Ready
SMS Ready
RDY
+CFUN: 1
+CPIN: READY
Call Ready
SMS Ready
</code></pre>

<p>The above data is continuously printing on console.</p>
 43604: <p>I am 90% sure it's a power issue. Not sure on what board/module you're using but the SIM800L/SIM900 needs a burst of current of 2&nbsp;A during 577&nbsp;µS (See the <a href="http://img.filipeflop.com/files/download/Datasheet_SIM800L.pdf" rel="nofollow noreferrer">manual</a>). </p>

<p>Try using 4700&nbsp;µF and a 10&nbsp;µF capacitor in parallel with the module. Powering it with a proper power source instead of the Arduino wouldn't hurt too.</p>
