Question:

Can I downgrade baseband 4.12.05 to 1.59.00 without SHSH blobs?

Answer:

The notion of SHSH has gained importance since the arrival of iOS 4.x.

Do not get confused between the SHSH for iOS with downgrading your baseband as these two are totally different entities.

You can always downgrade your iOS if you have saved your SHSH before, but baseband can never be downgraded no matter how. This is due to a complex security system called BBTicket which was implemented by Apple that prevents any attempt to do downgrade iPhone’s baseband.

So back to the question, can you downgrade baseband 4.12.05 to 1.59.00 without SHSH blobs? The obvious answer is no.

The best way is to get it officially unlocked using this service or here.