Got sim card today, Can I activate it in January?

Yes you can activate later on . There is no known limited time to activate

I think there is no deadline for activation

Anytime you wish. It doesn't look like there is an expiry date on them.

Beta price was extended for 2 more months. So intro price should be same. Then Jan should be fine.

No deadline. Give 'er.

Yes just make sure to do it before the price changes :)

No rush, considering the date for the introductory price has been extended.

You can activate anytime!

Yes but you risk to miss the introductory prices and pay more for your cell plan