Random route / trunk selection

Hello people,

after searching a lot on internet and not finding nothing… i come here to ask you…

i have my asterisk running with freepbx on a centos 4.6 box…

Asterisk: 1.4.18
Freepbx: 2.1.1

I have a lot of sip trunks that i pay for its plans, then i share these plans with my own clients…

Like:

[trunk1] 2000 minutes
[trunk2] 2000 minutes
[trunk3] 2000 minutes
[trunk4] 2000 minutes

These plans are 2000 minutes but if i use more than this i get suspended.

i want to make some way to randomize or make it on a logic sequence these trunks… like… when a extension make a call it uses the trunk1, when other gets it use trunk2, trunk3 and trunk4.

now it is always using the trunk1 and just jump to second when the first is in use.

i want to use more or less the same minutes on all trunks…

Thank you very much,

Diego Thomas