Doesn't seem to connect. I have international calling plan on my landline. I can call landlines in another country w/o issue. But I get an error message when trying to call cell phones in that same country. Why is that and can it be fixed somehow? I found comments that cell phones are terminated differently and may not work. But can work with perhaps additional per minute charges. But no info on how to get it to work.

Also, I assume that calling a domestic cell phone that happens to be in a different country still works fine - I just call the cell number like normal and don't need to know it's even in a different country at the moment. Right? Or is that now broken too?

I use 1-VOIP and do not have a problem connecting to overseas cell phones. It may be your plan. My Worldwide plan is about $30 a month with a very small surcharge when connecting to a cell phone. I also use Onesimcard for my international cell phone when out of the US. It is a Latvian cell phone number and fees from most countries are .02 to 1 cent a minute.

I have been out of the business for years.
So some of this may be out of date.

You landline services has two parts

Your local carrier (LECs)

You Long Distance Carrier (IXCs)

They may be the same companies or different ones.

Look at your bill, find your long distance carrier and talk to them.

They may have locked out international cell phones for fraud prevention or may not have a contract with the system you are calling.

It can also happen with cell phones.
My carrier was having a contract fight in Europe and my phone would not work in Italy.
but as soon a I crossed into another country it worked again.

I get confused with international phone numbers. I can get past the country code but when someone gives me their number, sometimes it only works when calling them from inside the country on a local number.

Some international phone numbers also have a 'city code' as part of the number that has to be included when calling it from the US.