Zaptel/Asterisk - configure for a different country?

We are using Digium TDM400 FXO/FXS cards in linux systems. We currently have them working in their default settings.

Now, we need to be able to ship working systems to various other countries and have them work. For example, we recently shipped one pair of machines to Dubai, and another to somewhere in India.

What do I need to do, in order to make these systems work in other countries?? I’ve looked through TFOT (which has a passing comment on zaptel.conf settings for loadzone, but doesn’t list the options, other than us). I’m assuming that Zaptel settings will only deal with recognizing the incoming line, and that I’ll have to do something else with Asterisk in order to generate valid signals back to an outside caller??

What would be most helpful to me would be some kind of tutorial with a title something like “how to configure your linux-based TDM400 system for another country”… does anything like that exist???

More recent messages are making references, both to
loadzone and defaultzone in zaptel.conf,
and to loading wctdm with opermode=country_of_choice.

is this all that I need to do, to support both sending and receiving calls??
Do I need the zaptel.conf settings, even if I use opermode?? or are these options redundant??