The Staff of the Securities and Exchange Commission Division of Trading and Markets issued advice on Securities Exchange Act of 1934 Rule 15a-6, involving registration exemptions for foreign broker-dealers.  See http://www.sec.gov/divisions/marketreq/faq-15a-6-foreign-bd.htm.

In particular, Rule 15a-6 activities include when broker-dealers

• effect unsolicited securities transactions; 
• provide research reports to major U.S. institutional investors, and effect transactions in the subject securities with or for those investors; 
• solicit and effect transactions with or for U.S. institutional investors or major U.S. institutional investors through another broker-dealer; and 
• solicit and effect transactions with or for registered broker-dealers, and in a broker or dealer capacity for others.

The Staff stated that Rule 15a-6 facilitates access and provides operational guidance, and addressed a variety of topics including, among other things, presence in the United States; global employee stock option plans, confirmations and account statement for unsolicited transactions on behalf of a U.S. investor; and the distribution of research to major U.S. institutional investors, among other topics. 

In short, this is a complicated area for foreign broker-dealers, who should consider U.S. counsel prior to undertaking these operations.