Quote from di1836:
why is it that some firms require traders to have a series 7 and some don't? what are the differences between these firms?
Many good answers already. Retail brokerages who hire employees that handle client funds (Scottrade, Schwab, etc), will require a 7 plus other licenses depending on your relevant functions at the firm. States may also require specific licenses in addition to the 7.
Currently, the props requiring a 7 are Echotrade, Bright Trading and HOLD Brothers, and perhaps others? Although you aren't handling "client funds" at these firms, their SRO (self regulatory organizations) require their traders to have a 7.
If you conduct due diligence, then you'll notice that the firms requiring their traders to hold a 7 are much better capitalized than other prop firms that are registered with CBSX only.
For example, according to the SEC.gov site database, Bright is probably the best capitalized among all the prop firms, with over $99 MILLION in total member's equity as of the end of 2008. Not sure about 2009, but damn, that's a lot of coin!