I'm an indian national who was studying in the US. I graduated in Dec 2011, and have been working at a company since Jan 2012 on F1-OPT. On Oct 1, 2012, my status changed to H1-B.

I've already filed my taxes, and not filled Form 8843. My tax consultant says I don't need to file it, since Schedule OI contains the relevant information (change of status, days in US etc.).

Should I send my Form 8843?

If you did not pay Social Secuity and Medicare taxes during your OPT period, you are required to file Form 8843.
Now you can not send form 8843 alone. For this you need to file amended tax return after waiting for alteast 8 weeks after filing original return.
Or just take no action. If IRS has any question, they will contact you. If IRS asks you to pay social security taxes for your OPT period, then you can file amended tax return.

Actually, in this case, I believe he should send the Form 8843 by itself. He just needs to print off the second page and SIGN it.