First I need to mention that I have no VOIP expirence with Openfire/spark. I did do some research when the SIP plugin first became available and I have a basic understanding of how it works.
I think you may be making the same wrong assumption as I did when starting my research. That is: openfire is not a VOIP PBX. I was hopping to have openfire be a magic plug and play corporate skype, but after my research into openfire, sip, and general voip technology I understood my mistake. Several of the features you list are specific to a VOIP PBX not to a SIP client.
A few item on your list specifically stand out for me:
Calling from PC to landlines and mobile phones
Calling from landlines to PC
Voicemails sent to email
Call forwarding
SMS
These, seem to me, to be features of which ever VOIP PBX you use not the SIP client you connect to it. I believe the openfire plugin is specific to asterisk
Why do I have to go to a support forum to know ‘some’ of your product’s features? Why don’t you have a list of features so I can decide whether your server / client / webclient is great or not?