Google Wave is currently an invite only service this means you will either receive a Prime Account from Google or been sent an invite from a Prime Account, this is currently the only way to access Google Wave.

The only difference between the two types of accounts is a Prime Account has eight invites to send to friends and a non-prime accounts get none, other than that all functions are the same.

This helps Google to manage the growth of Google Wave during the first few months of testing, over time it’s expected that all accounts will be able to invite friends.

If you want to learn more about Google Wave purchase my Ebook The Unauthorised Guide to Google Wave, it contains a good look at Google Wave Preview and some of the more advanced features included in over 20 pages.