that makes it a bit more involved
you need to advertise the group and then add the users from the second system to the group.
from then on it is like RodneyMcSnow or TomMills said, either create a shortcode that you can dial or do it with a button.
There is however a maximum of users that you can page at one time per system due to power constraints (I would think) and I can't remember the amount of phones.
Joe W.
TeleTechs.ca
FHandw, ACSS (SME), ACIS (SME)
“This is the end of the world, make sure to buy your T-shirt before it is too late"
Original expression of my daughter