Unless you have transposed or mistyped the Speed Dial 2 code in your previous post, I have no idea why what you did actually worked. (I am presuming from your first post you need to dial << *98 >> to access your voicemail.) If that is the case, why not try the following:
Set Code 28 in Star Code Profile A to << *98, Voice Mail, call(**1*98#) >>.
If you only have SP1 active, you can optionally leave out the << **1 >>. And, of course, you'll lose the original *98 star code (Blind Transfer) unless you assign it elsewhere.
Good luck.