I went through this analysis myself, as I travel to Canada frequently and also to Taiwan and Japan (with those trips probably becoming more frequent and longer stays). I came to the conclusion that giving ATT $75/m (and that was after a huge corp discount and bonus minutes) PLUS paying for voice and data roaming was not going to cut it.

I had a second phone I was using in Canada with Fido prepaid that I had setup to cost me nothing more than $2 a day (unlimited incoming calls, so I had my regular lines forward to home VOIP then forwarded to my Fido number), so I was already in a 'foreign SIM' situation.

I decided Straight Talk's $35/m savings was well worth it - I now have an unlocked iPhone I can use with Fido's $2/day plan and $10/60mb/week, and also use it for unlimited wifi calls using Talkatone. When I'm in Taiwan, I can use a local SIM or just do what I have been doing, and rely on Talkatone with wifi - and enjoy the fact I can't be constantly pestered with calls in the middle of the night.

I can use Google Voice to call abroad (which I was doing previously with ATT), and even though I lost int'l text and domestic MMS, everyone I text is already using Whatsapp, so I will just keep that option. In short, very little has changed and the only real downside is not being able to receive or make an emergency call while abroad - but I can work around that as needed.