Hey everyone, do yourself a favor. Go to e.B.a.y and search: "Replacement cable with Remote Mic connect iphone to Sennheiser HD598 HD558 HD518". There is a seller out of HK selling this cable for $17 CDN ($16 USD). I ordered and got it today and it works with the Momentum. It was a tight fit for the hole and I haven't been able to turn the cable's head in the hole to secure it like I did with my original cables. It is in very snuggly and I'm enjoying stereo sound and full iphone controls. I'm ordering a couple more cause I have no idea about the sturdiness of this cable and I make no claim about it's hardiness. I can get 5! of these cables for the price of one cable from Sennheiser. Save YOUR money.
I will report back and update if this cable fails under very common and regular use.
Fendercase