it is rather low, and it will tend to disappear. Indeed, the “CS-Paging while the MS is in Packet Transfer Mode” feature will tend to be done by the BSC more and more.
I’m sure that it is already done by most vendors (ericsson, etc.).
For example, alcatel is proposing this feature in B11.
(of course, the cost is not the same between adding an interface and upgrading the software…)