I have worked on kamailio for one year. It is a great open source Skype like solution.
Now i have to deploy a new solution with new requirements. Kindly suggest that what will be
the best open source application will fulfill my requirements. I need the following facilities:

Best solution, according my opinion will be own solution - solution developed for this purpose.

Ahead of all (voice) I would put Kamailio, behind (voice) Asterisk servers.

(1) Call Recording (Outbound/Inbound)

Asterisk servers, MySQL, some file server

(2) On Demand Recording

Asterisk can do it very well

(3) Dictation Service

Same as above

(4) Complex Inbound Routing

AGI scripts for Asterisk

(5) IVR (Interactive Voice Response)

AGI scripts for Asterisk + payed or free TTS engine. Better is to use free one, because payed are very complex with bulk of stupid limits, and "alternative" logic.

I am trying to be polite correct, and I have to use alternative, instead of lets say idiotic.

(6) Auto Attendant

Asterisk

(7) Client Recordings Mgmt & Playback Portal

AGI scripts + TTS

(8) Multi-level Client hierarchy / Subscription Plans

AGI scripts, PHP web site, MySQL behind all.

(9) Voicemail

I prefer own AGI script and voice mail

(10) Time based Routing (Message Box)

AGI scripts are very good

(11) Call Queuing & Conferencing

If you do not need video conferencing, again Asterisk is very good solution

(12) Bulk Download & Emailing

Perl scripts - but it depends. There are Python scripts for some cases, also there are LUA.

(13) Call Whisper

Asterisk can do it very well.

(14) Smartphone apps (SIP clients)

Android applications, based on some of GPL SIP client. Of course you will need to provide modified code.

Of course, there are lot of free applications, but I doubt, you will find exactly what you want, and this means - you will spend more time, to understand and modify ready application, then to develop own one.