Verizon showed a Spring road map today and it had a ton of 4G devices on it. SGSII was one of them. It said for MAY! Not to long now. I'm sure other carriers will be around the same time. I say between May and June. Last year they all were close around launch time. June will be for the Evo 3D. So I say several variant launches of SGSII during May. Could be late April. Then again Sprint might not want to over shine the NS4G. Either way its not to far off now.
Oh, and it'll be 4G flavored for Verizon, so I think it shall be that way for all carriers.