In my setup I am using CUCM 4.2(1)SR1b.I was using ATA 186 for all these days and now we have got ATA 188,I would like to know whether ATA 188 will be supported by this version or not.
Yes, you should be good to go with the ATA 188 (it will be added as an ATA 186 when doing the config) :)
Cisco ATA 186 and ATA 188 Analog Telephone Adaptor
Each release of Cisco Unified Communications Manager includes device support for Version 2.1.5.
Hope this helps!