The I9020A uses a different radio from the I9020T and I9023. The A uses 850/1900 UMTS while the T and 23 use AWS UMTS. The only update out so far is meant for the two AWS UMTS models.
It is possible to force the I9020T update to install onto the I9020A (as shown in the original post), but it involves rooting your phone and flashing several different files. I wouldn't recommend it for novices. Plus, we don't know how stable the final result really is.