The alternative is expensive and that is IPLC. It will cost 6600 USD per month for a E1 on IPLC. The quality will be higher and will be as good as traditional phone lines.
VOIP on a good IP connection is almost as good as IPLC. But you need to have a CIR consistency.
Packet losses in DSL and DXX circuits cause problems ; the bandwidth provided by PSEB in STPs is very good and generally suffices in lieu of IPLC.