Speaking to the original point of the thread.. I doubt that any tone paging would work on any digital system - be it ProVoice, Motorola ASTRO, or any other digital format. The whole concept of tone paging requires that the audio tones stay at the same pitch every time in order to trigger the receiving radios (or pagers/alert monitors). I'm no audio technician, but I am fairly confident that the act of converting the audio from analog to digital and then back distorts the pitch beyond what the receiver's tolerance (which is usually +/- a few hz, IIRC).
The easiest way to maintain paging when migrating to a digital system (trunk or otherwise) from an existing conventional analog system is to retain the existing analog conventional paging for that specific use only, as mentioned before. The downside is that you now have two distinct systems to maintain and upkeep, and the users have to hold onto two separate pieces of equipment in order to be alerted and be able to communicate.
My province is imminently moving to a P25 700MHz system and I'd like to see them go a different way. I personally think the volunteers would be able to be "paged" using a type of selective calling function that is already existent in most trunking/digital systems. Similar to I-Calls, it is possible to do a "Call Alert" (that's Motorola's term for it and I'm familiar with Mother M; M/A-COM may call it something else for EDACS systems). Just a little bit of product enhancement (which I'm sure a vendor would be willing to undertake, given a migration project of sufficient magnitude) would allow not only volunteers but all users of the system to be able to be alerted either as a group or individually using said selcall technology.
Kyparamedic: If you're simply looking for some kind of noisemaker to alert you that there's a call, i.e. a loud tone to come across the airwaves, I do believe that THAT kind of thing is still available. I'm not sure of EDACS systems in particular, because as I mentioned above, my main experience is in Motorola. But on our hybrid analog/digital trunk system, we can send the three typical Motorola noisemakers - solid tone, high-low alternating tone, and a third which I don't recall right now but might be a stuttered warbling tone - over any audio resource (channel/talkgroup), be it analog, digital, conventional, or trunked. If you're looking for something to selectively notify a specific crew of a need for their response, you need to look at selcall alerting.