It’s usually fairly easy to find out the current service pack level of a Microsoft Product. Normally, the product’s version information includes the information “Service Pack: #” or something similar. Not so with Exchange 2007. To find out an Exchange 2007’s service pack level, you must first find the build number and then compare the build number to this Microsoft KB article.
To find your build number from the Management Console select “Server Configuration”, right-click your server and select “Properties” and look on the “General” tab.
To find your build number from the Management Shell, run get-exchangeserver against the Exchange server in question. You will want to pipe the output into a different view to be able to see the full version number; for example get-exchangeserver | list. Look for the “AdminDisplayVersion:” line. The “Exchange Version” line, according to this article, refers to “the minimum version of the product that can read the object” and is not the number you need.
Then, compare the build number to Microsoft KB158530. As an example, I am running build 240.6 which equates to Exchange 2007 SP1.
For further reference, check out KB152439 “How to determine the version number, the build number, and the service pack level of Exchange Server”