Okay, Now that I have my morning coffee I can focus on this for a bit...
There are a few options depending on how sofisticated you want to be.. There are also some limits/caveats with some of the services like Google Voice that make certain things more difficult..
Option 1: (which is how I started out).
I had a T-Mobile phone with Seattle
, WA number and International roaming (T-Mobile One Plus). I connected a free Google Voice account to my T-Mobile number to handle voicemail and transcribe the voicemails which were emailed to my satellite email
and SMS'd to my cell phone. For incoming calls I could choose to take the call or let it go to voicemail and get the text transcription. I hardly ever listened to a voicemail. And then I could call back, text back, email back however I felt was appropriate. When out of range I would get the transcribed voicemails in my satellite email and could just reply via email if I had their email address.
I also set up a Skype account with a paid Skype-In number (also Seattle) and a paid unlimited outbound calling subscription. In Google Voice I set it up to forward calls to both my T-Mobile phone and my Skype-In number. Incoming calls would ring on the phone AND the Skype app and I could choose to answer either. Skype has a setting to configure outbound caller ID to match my cell phone so I could call out on Skype and it looked like I was calling from my mobile. Skype worked nearly flawlessly on the 256kbps slowed data speed I got from T-Mobile in other countries (LTE is only in Can, US, Mex).
Google Voice is free, but it can only forward calls to US +1 numbers. So if you want to forward to an Iridium phone you need to add a +1 number option to your sat phone (typically $10/mo addon).
Optionally you can set up forwarding in Skype to do the same, and Skype can forward to international numbers (but NOT Iridium +8816, so you still need the Iridium +1 option). Skype just uses your skype subscription or a credit that you set up to pay for the calls. Outbound Skype calls are about $0.02/min.
The Skype-In + Outbound calling subscription was about $12/month total.
I ran this way for about a year before switching our phones to Google Fi. Google Fi takes over your Google Voice account and some of the features are different..
Port Number to Google Voice... You can port your existing cell phone number to Google Voice and then set up multi-forward in Google Voice, as well as Voicemail transcription. When you do this your existing cell phone will be cancelled of course, but then you can get local SIMs, etc in other countries.
Since Google Voice can't forward to International numbers, you would need to do a couple of things.
Google Voice could forward to an Iridium +1 number AND a Skype-In Number. Then Skype could be configured to ring for 15 seconds or so, then forward to an International cell number that you could adjust as you travel and get new SIM cards. You'd pay for your local SIM card airtime, and you'd pay for Skype to call the International SIM card number if you don't answer via the Skype App before it forwards, but overall not a ton of cost.
If you called someone from your International SIM card, the caller ID would show that International number... But you could make unlimited calls to North America with a $6/mo subscription in Skype and have your old number (the one ported to Google Voice) show up on caller ID.
Option 3: (do some more advanced stuff)
Sea-Tech itself uses a service I am building for cruisers who are running businesses while travelling. It involves an internet based VOIP service. Sea-Tech's primary business number (the one on our website, business cards, ec) is actually a number I obtained through Skype (my original Skype-In number) and then ported to my current
VOIP service. For incoming calls to that number, the service routes the call to a full Interactive voice response menu that changes based on time of day. Menu options for sales, activations, accounting, support, etc. Depending on the choices the calls get routed to various forwarded phone numbers. Some are forwarded directly to a manufacturers support line, others forwarded to my cell phone. Some are important enough to ring on all staff cell phones (first to answer gets the call). I have ring groups set up that can forward to a sat phone, skype number, and cell phone so that no matter where I am a call can come through and I have a choice as to how to answer it. At night the calls go to voicemail and the voicemail audio file is emailed to me, and I have a second service that transcribes the audio and sends me the text of it as well.
Incoming calls are no charge, but I do pay for the outgoing forwarded calls, which add up to just a couple of pennies per minute. The nice thing about this is it's essentially a full PBX system in the cloud and has tons of features. Call queues, call rerouting, forwarding, ringing to multiple phones, etc, and it's a VOIP service so I can also use any old VOIP client on a smartphone, or a fancy VOIP desk phone and connect directly in to the system via the Internet.
My plan as far as business goes is to offer this whole package as a managed service to entrepeneurs who need to be reachable while travelling, but there is nothing stopping someone from just building their own using the same set of services on the Internet.
Hopefully that helps.. Feel free to ask questions, especially if I made anything a bit confusing.