VoIP related question: how do I call someone in another country over the internet and have it locally connect to a cell phone?

This would perhaps be best asked at r/VoIP, however I don’t have enough karma to post there. Sorry for bothering here, but I felt that someone might know what I’m looking for! Thanks.

I’m new to all of this. I’ve been reading about VoIP, ATA, PBX, PSTN, etc. and I’m sure what I’d like to achieve is possible, I just don’t know the name of the product I need.

There are three people involved here: myself, my associate, and my business partner.

Here’s the situation:

I’m in Europe and I have access to reliable internet. My associate is in East Africa and has very poor 3G (and barely 4G) connectivity.

Calls over data — of any kind — are hopeless. It doesn’t matter if it’s FaceTime Audio, WhatsApp, Skype, or anything else. Connections for my associate drop constantly.

I’d like to avoid racking up an expensive bill calling my associate through a traditional phone call. Receiving such a call would also be expensive for my associate so that’s not an option.

Now, I’m involved in building a small business network over in East Africa. In that location a fiber connection is available and it is generally reliable.

My business partner works at the location and has used a simple Wi-Fi AP to use the underlying fiber connection on an iPhone and FaceTime Audio calls come through perfectly.

Here’s the problem:

My associate moves around the country and rarely has a chance to be at the location with the business network setup.

My business partner however could be of use to setup something in the location, the question is: what do we need?

I’d like to be able to use my internet connection in Europe to call a <insert device here>, which would forward (or somehow connect) to my associate’s phone number over a traditional phone call.

Ideally, it would work in reverse: my associate calls the number associated with the <insert device here>, which then turns the call into a VoIP call or something similar, connecting to me here in Europe.

I don’t know the names of things or how they work. I thought maybe I could buy an Android phone for my business partner, who would connect it to the business network over Wi-Fi and then have some software do the magic (incoming VoIP is ”tunneled” into a traditional phone call to my associate’s mobile phone).

If I need to have my business partner swap out SIMs every now and then in the <insert device here>, that’s absolutely not a problem. Keep in mind only prepaid SIM cards are realistically available in the area.

What do I need and how does it work? Thank you a million for any pointers!