yes that is a true rumor. I have spoken with several regional reps from cingular and they have all said the same thing.
There will be a firmware update for the 8700 sometime this fall that will take the muti-function button and enable it to use PTT. They are still working out some bugs with the PTT network prior to releasing it to BB users.
You need to remember what company you are talking about. Cingular takes it's time doing anything. The last conversation I had with my contact it was stated that they would be ready for PTT on the 8700 in the September/October timeframe. Seems to me that they may be trying to introduce this option at the same time that Sprint introduces thier 87xx series.
ptt will be enabled on the 8700 when cingular releases the blackberry "stealth" that everyone has been talking about...btw, the stealth will not be umts capable...don't mean to rain on anyone's parade!
it's a cool new device, and i have had the opportunity to play with it for months now...