All the Ericsson products have a product number, which is of the form XXX nnn nn... RnX , where X is a letter and n is a digit. The RnX part is the revision number. The product number is printed on a small silver label somewhere out of the way on your product, usually under the battery or on the connector side of clip-on modems.
Note that Ericsson has a policy of replacing incompatible products. If you have a DI27 rev. 1 or 2, you may be able to exchange it for a rev. 3.