Maybe I didn't pose the question correctly. I am a telecom vendor and while I also sell a hosted solution I am wondering if anyone encounters complaints from clients because they lost a standard type PBX feature. For example one of my clients had an issue with delayed transferring. Took much longer than their PBX system. Using SIP phones that are not proprietary to the solution may cause a loss of certain features when using a phone (not PC). Loss of single button transfers, no extension appearances poses extreme frustration to end users.