All the features of PBX you will find with Asterisk, and by extension VoIP providers that run Asterisk IP PBX.
Some standard Asterisk features:
Many, many VoIP providers use Asterisk. Because it is free, openly developed, and compatible with just about every VoIP type, Asterisk is a good choice for running an IP PBX phone system.
VoIP providers often use Asterisk to supply PBX, but many VoIP providers that don't sell PBX services are still compatible with the software on the user's end.