Hi Djordje,
Alas, no. StringTheory is required by NetTalk, but is not included in NetTalk. So the math works the other way. For those who already have StringTheory (and most probably do judging by the StringTheory numbers) the upgrade is $299 while on special. For those that don't have it already, they will need to purchase that as well. Fortunately if you buy StringTheory at the same time as NetTalk there is a discount on it as well.
cheers
Bruce