There has been a rumor going around for a few days that arena season 4 will begin on June 17th. I actually heard this in Alterac Valley this weekend when I was plowing through the place with a few friends and tanking Drek and two of his generals.
While lots of folks wish it was different, season 4 will not be starting on the 17th. Drysc said as much today in a blue post, and went on to reiterate that they will still be giving a two week notice of any upcoming season.
Personally, I expect season 4 to start sometime in late July or early August. That gives it about four months of activity until the supposed release of Wrath of the Lich King in November. But even the release of WotLK in November is unconfirmed, and that's just my guess which is no better than any rumor you hear in a battleground. The only official word will come from Blizzard, which we'll have carried here as soon as we hear it.