The producers of
Tales of Symphonia are sure taking their sweet time with this anime trilogy. The final OVA series has just been
green-lit, but if the previous chapters' release timeframes are anything to go by, fans may not get to enjoy the fruits of this announcement anytime soon. After all, the current OVA
Tales of Symphonia: Tethe'alla Chapter still has two episodes to go. And if they'll take another 2-years break after this, like they did after the first ToS OVA... well, you do the math.

The third and final Tales of Syphonia OVA series will apparently be subtitled
Sekai Tougou-hen (The United World Episode), covering the story's ending chapter. The first two series were both produced by Frontier Works and animated by studio ufotable, so presumably these same companies will reunite for the final part.
The upcoming 3rd episode of Tales of Symphonia: Tethe'alla Chapter will be arriving later than expected, on September 23. Thus leaving the 4th and final episode for winter 2010. And then, Tales of Symphonia: Sekai Tougou-hen in... 2012? 2013? We'll see.