Change the customBinding in the web.config to use larger defaults. I picked 2MB as it is a reasonable size. Of course setting it to 2GB (as your code suggests) will work but it does leave you more vulnerable to attacks. Pick a size that is larger than your largest request but isn't overly large.
Check this : Using Large Message Requests in Silverlight with WCF
<system.serviceModel>
<behaviors>
<serviceBehaviors>
<behavior name="TestLargeWCF.Web.MyServiceBehavior">
<serviceMetadata httpGetEnabled="true"/>
<serviceDebug includeExceptionDetailInFaults="false"/>
</behavior>
</serviceBehaviors>
</behaviors>
<bindings>
<customBinding>
<binding name="customBinding0">
<binaryMessageEncoding />
<!-- Start change -->
<httpTransport maxReceivedMessageSize="2097152"
maxBufferSize="2097152"
maxBufferPoolSize="2097152"/>
<!-- Stop change -->
</binding>
</customBinding>
</bindings>
<serviceHostingEnvironment aspNetCompatibilityEnabled="true"/>
<services>
<service behaviorConfiguration="Web.MyServiceBehavior" name="TestLargeWCF.Web.MyService">
<endpoint address=""
binding="customBinding"
bindingConfiguration="customBinding0"
contract="TestLargeWCF.Web.MyService"/>
<endpoint address="mex"
binding="mexHttpBinding"
contract="IMetadataExchange"/>
</service>
</services>
</system.serviceModel>