public static synchronized SmsService getInstance()
    {
        if ( INSTANCE == null )
        {
            INSTANCE = new SmsService();
        }

        return INSTANCE;
    }
A service to send SMS messages.<p>

This class is configured with a set of Jive properties. Note that each service provider can require a different set
of properties to be set.
<ul>
<li>{@code sms.smpp.connections.maxAmount} -- the maximum amount of connections. The default value is one.
<li>{@code sms.smpp.connections.idleMillis} -- time (in ms) after which idle connections are allowed to be evicted. Defaults to two minutes.
<li>{@code sms.smpp.host} -- the host name of your SMPP Server or SMSC, i.e. smsc.example.org. The default value is "localhost".
<li>{@code sms.smpp.port} -- the port on which the SMSC is listening. Defaults to 2775.
<li>{@code sms.smpp.systemId} -- the 'user name' to use when connecting to the SMSC.
<li>{@code sms.smpp.password} -- the password that authenticates the systemId value when connecting to the SMSC.
<li>{@code sms.smpp.systemType} -- an optional system type, which, if defined, will be used when connecting to the SMSC.
<li>{@code sms.smpp.receive.ton} -- The type-of-number value for 'receiving' SMS messages. Defaults to 'UNKNOWN'.
<li>{@code sms.smpp.receive.npi} -- The number-plan-indicator value for 'receiving' SMS messages. Defaults to 'UNKNOWN'.
<li>{@code sms.smpp.source.ton} -- The type-of-number value for the source of SMS messages. Defaults to 'UNKNOWN'.
<li>{@code sms.smpp.source.npi} -- The number-plan-indicator value for the source of SMS messages. Defaults to 'UNKNOWN'.
<li>{@code sms.smpp.source.address} -- The source address of SMS messages.
<li>{@code sms.smpp.destination.ton} -- The type-of-number value for the destination of SMS messages. Defaults to 'UNKNOWN'.
<li>{@code sms.smpp.destination.npi} -- The number-plan-indicator value for the destination of SMS messages. Defaults to 'UNKNOWN'.
</ul>

@author Guus der Kinderen, guus@goodbytes.nl
xmppserver/src/main/java/org/jivesoftware/util/SmsService.java