Thanx bro...it helped me a lot.
I was trying other tools like sn writer, imei writing etc. but baseband version itself was unknown.
So needed to reflash nvram. Did it through spflash tool as suggested, flashed stock rom, baseband version got detected but imei was invalid, then set imei with mobile uncle tools, took backup of imei and reflashed xperia rom then restored imei.
Now all set to explore new xperia Z2.
By the way.... There is a thanks button.....