Want to migrate fom sccp to sip protocol for cisco IP Phone 7912

According to my experience and knoledge: the Cisco 2900 and 3900 series platforms have collaboration feature parity with the Cisco 2800 and 3800 Series platforms, so all of the following collaboration capabilities and solutions are present:
• Cisco Unified Survivable Remote Site Telephony (SRST)
• Cisco Unified Border Element
• Time-division multiplexing public-switched-telephone-network (TDM PSTN) and private-branch-exchange (PBX) gateways
• VoiceXML contact-center gateways
• Cisco Unified Communications Manager (UCM) media resources (allowing conferencing, transcoding, and Media Termination Point [MTP])
• Resource Reservation Protocol (RSVP) Agent
• Cisco Unified Communications Manager Express (CME)
• Cisco Unified SIP Proxy
• Gatekeeper

Cisco 3900 Series Routers

This process should work for you http://www.cisco.com/en/US/products/hw/phones/ps379/products_tech_note09186a0080094584.shtml

Cisco Telephone Power Brick

call cisco tac for a replacement.

Here are the instructions for configuring these units for 3cx

http://www.3cx.com/sip-phones/cisco-7940.html

http://www.3cx.com/sip-phones/polycom-soundpoint.html

Since the 3cx softphone worked well, I don't see why you couldn't configure each as for 3cx and make them work as well.

can somebody help me we have a Sip connection between a mitel 3300 and Cisco callmanager only the conference call doesn't work who can help me out

Well, in most Cisco VoIP phones those lights are used to tell you if you have a voicemail. Have you checked your vm and cleared any new ones? This might be your issue ;)

Try configuring CCM IP address either trough DHCP parameter, or Network configuration on the phone.

Can you please make sure that you can ping the device - you might have a routing problem

I believe I saw somewhere that the 7920 works best with the 4.02 version of firmware... only hitch is you can't get it unless you have a valid Cisco login with access to their voice stuff. You could see if your local partner could get it for you otherwise. Also, I think you need the cradle to upgrade the phone manually - otherwise you need a TFTP server set up and the proper keywords in the cnf.xml file. There is better info on voip-info.org about these sccp phones - god I wish they (Cisco) would release a SIP firmware for these things!

Is the phones registered to CallManager or CME?
if CM, then it could be because of partitions and Calling Search Spaces. PTs are placed on the line and are restricted by CSSes. http://cisco.com/en/US/docs/voice_ip_comm/cucm/admin/4_1_3/ccmsys/a03ptcss.html#wp1020642

If it is CME, then it could be a configuration issue
http://cisco.com/en/US/docs/voice_ip_comm/cucme/roadmap/itsph.htm