mapplayer is right, only when you leave the company, you can transfer 401K into IRA or Roth IRA account in any broker. When the company may have different 401k mgmt policy, ask your HR.
YES, YOU CAN ONLY ROLLOVER YOUR 401K TO IB OR OTHER BROKER WHEN YOU LEAVE YOUR COMPANY.
OR, WHEN OTHER COMPANY BUY YOUR COMPANY AND THEN YOU CAN ROLLOVER YOUR 401K TO BROKERS.