OK, I think I'm ready.
Okay... given you're already on Ring Plus and your numbers are tied to Google Voice, truthfully? Going PAYG isn't really going to get you much cheaper than $5/month anyway (P'tel being the cheapest per minute PAYG offering available for your handset at 5¢ with a minimum monthly cost of $5, Airvoice and Spot can get you down into the $2.50-3.50 range, but run 10¢/minute and can include additional monthly costs. If you're getting under that threshold (or think the RP $6 Harrison plan is viable), you might want to re-evaluate the value of keeping the devices in your life at all. If you'd rather keep them around and given your current setup, you might as well ride out the RP gravy train for as long as it lasts or fits your needs. The only compelling reason to switch up services at this point is to switch for the sake of stability and customer support, and those changes may lead you to spending more than you are currently. I believe in quality over quantity and paying for what you need, and if you're on board with that, I'll be happy to help optimize accordingly; otherwise you've already taken things about as far as you can.
The VOIP.ms+CSipSimple idea is very viable, and if KakaoTalk is working for you, go for it. The Kik, Nimbuzz and XMS recommendations are primarily based on a measure between terms of service, privacy policy, platform availability, and overall data compression/usage on messaging. They're the least offensive and software stable click-and-install messaging apps I've found short of configuring your own using XMPP.
As to the Korea situation, so long as you have proper SIP account credentials, you can roll it and VOIP.ms into a singular device by using an ATA that supports two SIP accounts on one FXS port, like the OBi100. Then you can just set up dial plans to route the Korea calls through the one carrier and the remaining through the other. More specific advice would require knowing who the current VoIP provider is. You can PM me if you'd rather keep things a bit more private on this point.
Glad to be of help, and hope this gives you a bit extra direction.
What does it mean to be "without partner roaming"? Does that mean if I travel, I might have no phone service?
It means that on AT&T postpaid, you typically get free roaming onto T-Mobile/Plateautel/Cellular One/Cincinatti Bell/i wireless/[insert other obscure regional carrier here] GSM towers if there are no AT&T GSM towers available. On prepaid MVNOs like Airvoice, you can only make calls on AT&T towers. With major metropolitan areas and interstates, this typically isn't a problem as there's consistent coverage... and being on an AT&T MVNO, you're going to have a
far larger coverage map (even in the sticks) than any T-Mobile MVNO, and honestly there aren't many places there's a T-Mo tower where there isn't an AT&T one. The only minor exception to this rule is some of those regional players I mentioned above who have a bit of a spectrum lock in
parts of some states (mostly in more rural areas), like Plateautel (New Mexico, Texas panhandle), i wireless (Iowa), Cellular One (Illinois), Cinty Bell (Indiana, Ohio); you go into one of these areas, you're not likely to find many AT&T towers for making calls with on your prepaid plan far off the well beaten path.
Now, don't let this scare you off! As long as you have
map coverage for all the areas you'll typically find yourself, you'll most likely be fine. And even for the times you don't have AT&T coverage and you need to make an emergency call to 911? The nearest GSM tower,
no matter who owns it, has to take, route and connect your call to the nearest
PSAP for your reception area. You might not be able to call a tow truck or kindly old Aunt Harriet to let her know you'll be late, but if the engine is on fire or you broke a limb, you'll be able to call emergency services. Make sense?
I did confirm on h2o that you can add another phone. Thy give you $10 off each additional phone plan and the plan details are tied to each specific phone. No sharing of data etc.
Clarification for others: $40+ plans only, and it's been available since April. The deal is underwhelming at best. There's better family plan options on the GSM spectrum than H2O... interestingly enough, is's Consumer Cellular since the AT&T MVNO price restructuring.
I'm probably going to go with republic.
You made your choice, good for you. Stick with it and get on with your life and stop debating further, as you've already wasted several hundred dollars in opportunity cost since June as is. I hope it works out for you, and you don't get burned by their terms of service with your data usage.
Be well.