Asterisk 1.2 VS Asterisk 1.4

What is difference between Asterisk 1.2 and Asterisk 1.4
jsmith post on version 1.2 vs 1.4 :

Asterisk 1.2 was branched in November of 2005, and since then has only received bug fixes (with a few minor exceptions). You'd really only want to use it if you have specific problems with Asterisk 1.4 that keep you from using it. In August of this year, Asterisk 1.2 will no longer be supported, except for security updates.

Asterisk 1.4 was branched from the trunk in December of 2006. Like 1.2, the 1.4 branch is only getting bug fixes at this time. Asterisk 1.4 *should* be stable and production ready, but a few people are still having some issues with it, and are still running Asterisk 1.2. Personally, Asterisk 1.4 is working great for me, and I'm recommending that people give it a try.

and Asterisk 1.4 unveiled (by Tom Keating) and from few links (check below).

• Asterisk 1.4 แยกมาจาก Asterisk 1.2 (November 2005)
• quality, performance, scalability and interoperability improvements
• 20 new functionality เช่น
  • FAX
  • Jabber/Jingle/GoogleTalk (all relate XMPP) .. IM feature :)
    
  • Unified Messaging (UM) (faxes, e-mails and voicemails into a single mailbox)
  • Generic Jitter Buffer
  • Asterisk Extension Language Version 2 (AEL 2)
    
  • T.38 for FAX
  • New sound files and new language, of course - better quality!
    
  • Whisper Paging อันนี้ไม่รู้ว่าคืออะไร?
• variable length DTMF support
• centralized RADIUS storage for call detail records
• RTCP support
• RTP packetization
• menuselect (graphical module select tool similar to the kernel config system)
• Shared line Apperance support ( What's it? I don't know)
• Asterisk Builtin mini-HTTP server
  

Relate Links
New Asterisk Set to Ring
Digium Unveils the Latest Version of Asterisk
Asterisk 1.4 unveiled
New in Asterisk 1.4
Practical Asterisk 1.4 (unstable)