The Mini automatically checks for mail at power-up, whenever something is sent (message, sent track point, or whatever), and at one-hour intervals. AFAIK, the interval is not adjustable and the feature cannot be disabled.

Edited to add: In order for contacts to work after ANY change, a sync is required. This never happens via the Iridium network because the data volumes are too high. So I don't think that adding contacts on the device itself (in the absence of cell coverage) can be made to work. Newer devices which use the Explore app allow the creation of contacts in Explore, as well as bi-directional sync via the cell network. But a cell connection and Internet access is required. And the Explore app does not support the Mini.

If you need to send a message to someone who is not in your contact list, the only alternative is to type the full recipient address with the message.

The Mini is supported via the Earthmate app. The Earthmate app does allow you to request a message check via the paired Mini. There is no reason for this to require a cell connection. OTOH, I have not tried it myself.  AFAIK, the Earthmate app does not support manipulation of contacts in any way.

Thank you for your response.
I wasn't aware that it automatically checks for mail every hour. Thanks for that info. At least it has that.

It is a bummer there is no reasonable way to sync via the Iridium network to add a contact.

I'm not sure what you mean by "If you need to send a message to someone who is not in your contact list, the only alternative is to type the full recipient address with the message."
Could you elaborate please? 

Hopefully at least the Earthmate app comes out with an update to include add/edit contacts.

Thanks again, your help is most appreciated.

When you send a message with the mini, you start with the Select Contacts option This shows you a list of your contacts from which you can select one or more. At the very top of this list, there is an option for Type Contact. If you select that option, you will see the Mini's "virtual keyboard". Here, you can type the email address(es), SMS phone number(s), or inReach address(es) of the people who are not in your contact list. I believe (but don't recall for sure) that multiple addresses are separated by commas. SMS numbers must include the dialing code (1 for the US and Canada, for example). Don't recall if the leading + is required. Sorry for the vagueness - but I just don't remember and don't want to mislead.

Pretty sure you can use this in conjunction with selection from the contact list. That is, you can have contacts and manually entered addresses on the same message. Be aware that using individual addresses this way cuts into the message length. Contacts are sent a small "codes" rather than as text. This is why both the Mini and the server must agree on the full contact list. Addresses which you type explicitly are sent as text. So they take up more "space" in the message to be sent via Iridium.