How to use 2 pstn channels

I've managed to setup my new ap100 card with 2 fxo channels.
In the zapata-auto.conf I see the 2 channels and in zapata.conf I have a group=0 which include all the settings which seems to work fine.
I have setup 2 Zap Channel DIDs with the 2 pstn numers.
I setup 2 trunks. I've called both z0 and choosed z0 as Zap Identifier. I'm not sure of this.

I'd like to use the second pstn line , channel 2 , to call the mobile phones .
I've done two outbound routes and use the second one for calling mobile phones with a proper dial patter.

When I try to call a mobile phone, the channel 1 is used instead of the channel 2.

how I can select the zap channel to use in my outgoing calls?
should I do 2 groups in the zapata.conf ?

I've found no documentation about this. I hope for someone's help.

thanks