ASTERISK-IM connect OpenFire BACKEND to Asterisk to synchronise openfire user presence with asterisk's user extension. aka if the user is on phone in asterisk, his Spark status will change to On Phone also.
Sip phone I suppose permit to connect Spark client like a softphone into a SIP server. Both plugin can be used separatly or together
Asterisk-IM is like Jean said. It displays your presence (On-Phone) inside your IM client. It will also dial a call to another user for you if you right click on their name and click call. It will ring your extension and then theirs. This requires a phone hooked up.
SIP Phone Plugin actually turns your SPARK into a SIP Softphone. You must install it on the server side and on SPARK.