Configuration files such as sip.conf, iax.conf etc. can have hundreds of entries; such files are difficult to maintain.

Take a typical sip.conf, for example:

[201]
username=201
secret=1111
context=default
type=friend
qualify=yes
host=dynamic
canreinvite=no

[202]
username=202
secret=2222
context=default
type=friend
qualify=yes
host=dynamic
canreinvite=no

[203]
username=203
secret=3333
context=default
type=friend
qualify=yes
host=dynamic
canreinvite=no

There is another way. Asterisk offers the little-known support for templates! Using a template, our sip.conf would look like this instead:

[my-phones](!)       ; This entry is the template
context=default
type=friend
qualify=yes
host=dynamic
canreinvite=no

[201](my-phones)     ; Station 201
username=201
secret=1111

[202](my-phones)     ; Station 202
username=202
secret=2222

[203](my-phones)     ; Station 203
username=203
secret=3333

This is particularly useful when you have groups or classes of stations with very similar characteristics; that is, in cases where it isn't possible to put all the common parameters in the [general] section. Even in this small and simple example, we've managed to save a few lines and centralize future changes to the "class" my-phones.