The Telco Research TRU System (recently acquired by Peregrine), the ISI Infortex Rodata System, and the Microtel Microcall System are three CDR systems that I've experienced as working well with the G3.
All three have a proven track record of consistently dependable, reliable, accurate call tracking from my experience; the environment I'm familiar with has had them running 24x7x365 for anywhere from four to eight years, depending on the platform and when the office it's in was opened. They typically handle anywhere from 5K to 150K calls per day, again depending on the office where they are installed.
Like most call accounting system platforms, there are distinctions among their features, capabilities, and user interfaces that are mostly a matter of personal preference and budget size.
Based on the installations in the environment I'm familiar with, TRU differs from Rodata and Microcall in that its database isn't part and parcel of the application itself. It relies on a separate Foxpro database. There were some database stability issues with that system during startup.
All three companies have been pretty good at providing technical support, maintenance, and repair. I found them particularly responsive during Y2K readiness, and among the companies I found most proactive in understanding and protecting their customers interests during this critical period. Many major equipment vendors and service providers should have aspired to similar levels.
I have no experience with using them for billing chargeback or phone bill allocation. Each system offers this to varying degrees, with some level of functionality part and parcel of the basic package, and more available as a custom feature. (While I've experimented with the functions enough to know what's there, I've no experience with loading tariffs, etc., and can't speak to that.)
I have experience with using TRU in a remote polling mode, to cover multiple PBXs with the same central system; both the polling PC and the buffer boxes work well. I only have experience with Rodata and Microcall in a dedicated standalone mode, though believe they offer similar distributed capability.