Want to buy new Android Phone @ 10k..few issues i want to clarify..

Less budget phone tend to have less internal memory, Hence less apps.
I have entry level Android Samsung Y S5360-GT which has 190 mb internal memory which is very less but there is a way out to store apps in sd card.
-Root phone
-partition your sd card using mini partition wizard
-use one partition to store apps & other partition for your personal data.(using link2sd)

For most of the phones that I know of, you can extend the memory of your smartphone through micro SD card. It acts like your slave HDD (in computers). You can install and run your apps right on your external or internal memory without any issues. I'm not sure if this changes for a few apps.

Whether both SIMS operate at the same time will depend on the model (that's what I know, never used a dual SIM phone). Do you have any specific model in mind?

I know i can rooting is an option,but the warranty gets void if I root the phone.
#-Link-Snipped-# So you are saying that internal memory shouldnt be a focus pt while buying a smartfone?
I'm thinking of buying either Galaxy Duos Lite or Galaxy Ace duos. Do u have any idea? Can i recieve calls on the other sim while messaging on the first sim? and vice versa?

ankitfranciscanI know i can rooting is an option,but the warranty gets void if I root the phone.

Rooted phone can be un-rooted too.
Partial knowledge is dangerous than NO knowledge.