Need Buying Advice For Smartphone Under ₹7000....:-D....Anybody Help....!

638 isn't just worth it. It can't handle the games even though some are there. Neither is Omega.
The best option you have is Moto E.
I've used a lot of Lenovo phones and I haven't experienced hangs, even in the long run, but ppls personal experiences always differ.
Another good option is the Android One triplets (Canvas A1, Sparkle V and Dream Uno) which come around 5k now, thus giving a wide gap for accessories. They also have guaranteed updates.

And what about omega 5.0?
And there r many gameloft games in windows store,so if i will go with lumia 638, then can i play modern combat 5 in lumia 638? I m just excusing for lenovo bcoz my frbd told me dat it hangs too much.

EA doesn't make mobile games for W8, so MS is out of the question. (Their phones aren't v.good for gaming either)
That leaves you with two good options:
Lenovo A6000: It is a quite good all rounder phone, with a 5-inch screen, Snapdragon 410 processor, 1GB RAM and 8MP camera. However, availability of stocks may fluctuate.
Moto E 4G: This is also a really good phone if solid build, pure android and battery life is a priority. It has a 4.5-inch screen, Snapdragon 410 processor, 1GB RAM and 8MP camera. The small screen, VGA front camera and lack of flash for primary camera might make you winch, but it is currently on offer for just 6000 and also has a great exchange offer.

Until the offer lasts, I would recommend Moto E 4G. However, if you miss it, you'll be happier with the A6000.