Normal DISA using public phones and hence the auth. process is a MUST.
In this case, the access to DISA is limited to a few known phones, which could be "verified"by their phone number. The pin might be removed. Of cause, for more security, pin could be needed. The key point is you know the trade-off between risk and convenience.
Elastix Asterisk server, most of config and operation are in GUI interface.
go to original website http://elastix.org
you can download the source installation disk with 32/64 bit ISO
and user manual "Elastix Without Tears" http://elx.ec/ewt
or you can goto youtube.com search elastix