Lot lot things , i feel i missed a lot because i didn't write timely
A) The best is qtopia's full open source phone: yep qtopia relased full source code.
Link : http://qtopia.net/modules/devices/
B) The worst is Vonage's Loss on IPR issue: read the Patent and felt sad to the people who allowed it to be a patent ( ex: a server which responses to queries to translate uri to a phone no: etc ). I wonder its just an application of database and its a server - i don't know its a database server - ODBC can do this, or if the patent is for combination of server, transaction etc then DNS do it. I belive the patents need to be more better.
C) Exciting ones ?
Yep its telepathy : http://telepathy.freedesktop.org/wiki/
Look at http://laptop.org/laptop/ . An excellent stuff. I really love to get one or some hands on this for some time.
Look at N800 from Nokia: a full Linux tablet. An excellent device to have potential to replace all mobile phones in future with Wimax with sprint ( Sprint CEO stepped down - so what 'll happen to the wimax project ). Acanac offerd me one for free ( thanks to them - they are my VOIP provider )
Both uses telepathy and jabber.