i think WMA 2.0 defines system property wireless.messaging.sms.smsc for SMSC which you can retrieve
String _smsc_Number= System.getProperty("wireless.messaging.sms.smsc");
Same way you can set System.setProperty("wireless.messaging.sms.smsc", "+232131232131");
i haven't tried it but i think it should work.
give it a try:)
Cheers
Rawat