Hi Jerônimo,

> As fair as I understand, ofono gets the correct APN settings using
> Gnome Service Provider Database.

Not necessarily.  Mobile Broadband Provider Info can be used, but the
provisioning system is plugin based.  You can write your own if you
wish.  See examples/provision.c in oFono git.

> 
> My questions are:
>  - How can I 'tell' ofono to use a specific APN settings?

One can edit context settings via the D-Bus interface, if that is what
you mean.  See test/create-internet-context for an example.

>  - It seams that ofono only works if is started after usb-modeswitch
> detects the modem and create /dev/ttyUSBx devices. Is there anything to
> do to configure that to work properly? 
> 

As long as the modem is configured by usb-modeswitch properly and
detected by udev, the order of events doesn't matter.  oFono will detect
"hot-plugged" devices.

Regards,
-Denis