They're not a US-based company, but you can trade US stocks through them--and not just 4 round trips every 3 days, or whatever the rule is. I believe they get around the PDT rule by being based offshore (Jamica). I don't know anything about them, but I remember hearing about them when the PDT rule first came out, so they've been around for a while. I'm pretty sure that your funds are not SIPC protected, so just hope they don't go belly-up!
I was also looking for an offshore broker that allowed PDT with sub $25k balances. I found that Alliance Investments site linked above and realized that it had not been updated since 2004.
Further investigation found that they changed websites to www.allianceinvestment.com/. Now this site seems to still be up to date but no longer mentions PDT for sub $25k and no longer seems to offer any real time trading platform. They now only offer a web based platform.
I did email them asking if they still offered the old platform but never got a response back.