Which web service helps to find mobile phones according to custom criteria of specification? For example processor, memory, dual sim etc.
I'm gonna give you the short and simple answer.
you can also use a reputable shopping site (such as amazon) and use it's filters to find a phone
one more alternative is Google's Android phone browser (if you want an Android phone) http://www.android.com/devices/
gsm arena and so many on the web
you can try :
this website does it pretty well
Found another article on MakeUseOf about Amazon Wireless Comparison which can be used for the same thing.
flipkart is the best... you can try gsmarena also
Try CompareIndia | http://compareindia.in.com/
and Flipkart | http://www.flipkart.com/
They have feature & specification filters. If you are thinking of ordering online, Flipkart is probably the best Indian online shopping site.
You can check the phones online, but still wouldn't recommend an online purchase, as you can usually negotiate a much better discount over the counter sales. That is how I usually go about it. Check all the infos and tech specifications, over the internet, get a fair idea of the best discounts going on the internet and then go to a shop and bargain real hard. 99.99% of the time I get a much better deal.