Might be simpler way to do this, but it works.
If you are using a ContentObserver in Android to detect when there are new downloaded MMS messages, then you might have noticed that it is apparently not possible to get the sender information. A ton of stuff is available, but not the sender. However, the sender is provided when the MMS notification is received - and you can get this notification by using a BroadcastReceiver.
The only way I've found to get the sender once the MMS downloads is to use a separate database that stores the (transactionID, sender) when the MMS notification is received. Then, once the MMS has downloaded, you can use the transactionID which *is* available and look up the sender in the separate database.