John Emms used the name "Open Samisch" in the "Easy Guide to the Nimzo-Indian" (Presumably 4.a3 is the "closed" Samisch.) Indeed if you google "open samisch" there are a few hits suggesting that this nomenclature is not unique to Emms.

I dont consider myself an expert on these positions, but I will make one more post. Some liens in pgn that I attached had some errors where I blindly followed book and not even Houdini discovered the error sa tfirst sight, but there was better moves for both sides.

If black wants to play something that that is more soild than the pgn line I posted black can also play

[Event "Blitz:5'+2""]
[Site "Eskilstuna"]
[Date "????.??.??"]
[Round "?"]
[White "New game"]
[Black "Houdini 1.5 w32"]
[Result "*"]
[PlyCount "32"]
[TimeControl "300+2"]

1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4.
f3 c5 5. d5 O-O 6. e4 d6 7. Nge2 (7. Bd3 b5 8. Nge2 (8. dxe6 Bxe6 9. cxb5 a6
$44) 8... Nbd7 9. dxe6 fxe6 10. cxb5 Ne5 $13 11. Bf4 (11. O-O a6 12. Be3 d5 13.
exd5 exd5 14. Bg5 Nxd3 15. Qxd3 Bb7 $44) 11... Nxd3+ 12. Qxd3 d5 13. exd5 exd5
14. O-O d4 15. Ne4 Nxe4 16. fxe4 Be6 $44) 7... b5 8. Nf4 {Shirov} (8. dxe6 Bxe6
9. cxb5 a6 $44) (8. Ng3 Bb7) (8. a3 Ba5) 8... e5 9. Nfe2 Nh5 {
unmentioned by Yakovich} 10. g4 (10. cxb5 f5 $36 {Marin}) 10... Qh4+ 11. Kd2
Nf4 12. Nxf4 exf4 13. cxb5 a6 14. bxa6 Bxa6 15. Kc2 Bxc3 16. bxc3 Nd7 $44 *

Thanks for the input. I will have a look at it

Some quick lines in b5 line if anyone is interested. Quick look indicateds that blacks position is very playalbe. I can not give the entire chapter but they seems to improve over Yakovich at several points. I dont have Yakovich book myself but they have references to it in the article.

Klick wrote on 03/01/11 at 16:31:45:

O.K., maybe this was another unanswerable question of mine. There had been many. 
Then I'll try to be more exact.

How do you think the concrete variations following 5.d5 Nh5 are good for Black?
Or is it better to strive for a Benoni-type position?
(Even if it is a strong reply, I don't like Klick's suggestion, the look of the Blumenfeld-like 5..b5 whatsoever.)

I hope I have not asked this yet... 

I am constructing my Nimzo repertoire.
4.f3 c5 is my choice as Black 
(because I prefer 4.a3 Bxc3+ 5.bxc3 c5 6.f3 Nc6 7.e4 d6 over 6..d5 7.cxd5 Nxd5 etc)
but I don't know much about it.

What lines should I pay the most attention to? (any recommended model games?)

It's been my experience in CC that 4...c5 is vastly superior to 4...d5 against the 4. f3 variation. Here's an example of my own usage of 4...c5 to reach a winning endgame against my CC opponent on ICCF:

1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.f3 c5 5.d5 O-O 6.e4 d6 7.Bd2 exd5 8.cxd5 Nh5 9.Qe2 f5 10.O-O-O Re8 11.Nh3 Nd7 12.Qe3 Nhf6 13.Ng5 Nb6 14.Bb5 Re7 15.Qf4 h6 16.Ne6 Bxe6 17.dxe6 a6 18.Bd3 fxe4 19.Nxe4 Bxd2+ 20.Rxd2 Rxe6 21.Nxf6+ Qxf6 22.Qxf6 Rxf6 23.Be4 Ra7 24.Rhd1 Nc8 25.Rd5 b5 26.Kb1 Kf7 27.g4 Ke7 28.g5 hxg5 29.Rxg5 Kf8 30.Rh5 Ne7 31.Rh8+ Kf7 32.Rd8 Nf5 33.Rg1 Ke7 34.Rg8 Ke6 35.Re8+ Re7 36.Bxf5+ Rxf5 37.Re1+ Re5 38.Rxe5+ dxe5 39.Ra8 Rf7 40.Rxa6+ Kd5 41.Ra3 Kd4 42.Rb3 g5 43.Kc2 c4 44.Rxb5 Rxf3 45.Rb8 Rf2+ 46.Kc1 g4 

I've got a won endgame position after the 46th move. Below is another ICCF game where I have white and have reached a winning position quite quickly versus one of the 4...d5 lines:

1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.f3 d5 5.a3 Bxc3+ 6.bxc3 O-O 7.cxd5 exd5 8.e3 Re8 9.Bd3 b6 10.Ne2 c5 11.O-O Ba6 12.Ng3 Bxd3 13.Qxd3 Nc6 14.Bb2 c4 15.Qe2 h5 16.e4 dxe4 17.fxe4 h4 18.Nh5 Nxe4 19.Qxc4 Qd7 20.Rf4 Na5 21.Qd3 f5 22.Raf1 Rf8 23.Rxh4 Rae8 24.c4 g5 25.Rh3 g4 26.Rh4 Qc7 27.d5 Nxc4 28.d6 

I've in fact reached many winning and nearly winning positions when black opts for 4...d5, while 4...c5 leaves white with a lack-luster middlegame battle. I just don't understand why d5 remains the 'main' line when c5 is clearly better in meeting the 4. f3 variation.

Everyone is quoting Yakovich here but a more recent source os Moskalenko's "revolutionalise" book where he spends many pages analysing 4.f3. If i remember correctly in the last pages he gives some variations as unclear without tring too much for White but i would expect from you at least a discussion of his ideas.

Btw, Kramnik played 4.f3 with White yesterday in Wijk aan Zee!