After trying Conversation for a few days on my E71-1, I would like to make the following comments:

1) The idea of bundling Conversation together with the Contacts list IS UTTERLY stupid. It should've been bundled with messaging as a user can't simply start a conversation UNLESS that user already has one existing with another user.
2) Conversation does not show the entire exchange of messages with ALL text, like what the Treo's messaging platform has been doing EVER SINCE the beginning. A preview of each message isn't enough, as one needs to OPEN EACH AND EVERY message in the conversation just to know the complete context of the message.
3) Conversation does not take over as the default SMS handling application. It really FEELS STUPID to use Conversation outside of the messaging framework - e.g you can send SMS via Conversation but you CANT RECEIVE SMS on it, and still have to go to Messaging.

The only saving grace I found about Conversation is that it attempts to be simple. No conversation bubbles like what the iPhone does, and after indexing messages, it goes really fast.

I really wonder what are the developers thinking about making this a really competitive product. In short, at this point of development, I really cannot recommend installing this product as the product design of this application is highly questionable.