Freeswitch on latest FBSD

I am testing Freeswitch on FreBSD.

I have Dell Precision workstation with Xeon quad processor 2.66 Ghz. I have installed the latest bsd.
Then I compiled freeswitch on it and made load test. I am sending 800 simultaneous originate calls.
Then, FBSD can create only 1400 threads and the rest of calls are dropped.

I have run small utility to test how many maximum threads this box can reach to. I have got only 1400 threads. Later on, I ulimit everything to maximum with
ulimit -c unlimited
ulimit -d unlimited
ulimit -f unlimited
ulimit -i unlimited
ulimit -n 999999
ulimit -q unlimited
ulimit -u unlimited
ulimit -v unlimited
ulimit -x unlimited
ulimit -s 244
ulimit -l unlimited
ulimit -a

but the result is same, only 1400 threads maximum.

how can I increate this limit?

By the way, an ubuntu on old amd processor can reach up to 15000 threads. 

How can I tune this quad box?

Thanks

Erol Akarsu