True PRI, when working the audio quality and reliability is rarely an issue. But true PRI is getting very rare as it is more expensive for the providers to provide in local exchanges and to customer premises. Increasingly, any PRI to customer premises will actually be SIP somewhere upstream.
SIP is almost 25 -years old now and yet it still hasn't settled down to be a mature and stable technology. People keep adding new bits, competing bits, conflicting bits, onto a huge pile of standards that each SIP provider then implements and interprets differently. PRI had the advantage of being a set of standards that telcos agreed between themselves before any new standard was published. SIP on the other hand is open to every man and his dog and if an idea gets enough supporters it gets an RFC.
Rant over. SIP is here to stay, whereas PRI is going away. Get used to SIP.
Stuck in a never ending cycle of file copying.