Our scenario is the following:

Within One System:
When one user dials the extension of another user, the recipient's station answers handsfree speaker like you referenced

Between Two Ip Networked Systems:
When one user dials the extension of another user, the recipient's station rings and the call is connected only when the recipient presses the speaker key or picks up the handset. Ideally we would like this function to behave the same as if it was all within one system.

Also, is it possible for a user at Site A to have BLF status on his Avanti Memory key for an extension at another IP networked location?