It's a Java API that allows you to send SMS messages.
Yes. The easiest way is to use SmsSender.sendWapSiPushMsg() or .SmsSender.sendWapSiPushMsg()
Yes. The easiest way is to use SmsSender.sendMmsNotification().
Install the javacomm api from sun.
WMA is targeted towards J2ME.
smsj is targeted to create different types of messages. jsr212 is more focused on the sending part.