I think it would be worth reducing your resistance to the idea of 2 phones

If one of them was on 3 or T-mobile UK, the roaming data rates in Europe aren't much over £1 per MB, and if visiting the UK a callthrough provider could be used to USA for 3 pence a minute, perhaps then reserving callback use with the other SIM for the rest of Europe

I have had 2 phones for several year now.

1 local dutch prepaid to trigger a callback and 1 roaming free cellphone.

Using pbxes and smartvoip (betamax 6 eurocents to +44 mobile numbers) I trigger a callback by calling a voip did number
Than my roaming free cellphone receives a call and I have a dialtone.

Calling fixed numbers will cost me around 7 cents per minute and mobile (europe) between 10 and 20 cents.

Works very well.
pbxes also has a webcallback feature where you can fill in any number where you are at that moment. You will be called on that number, type your pincode and receive the dailtone. This way your can receive a callback in your hotel, freinds house wherever.

I guess you can use the free roaming sim like ekit in Europe to trigger the callback, or it doesnt work on it?

Do they present a CLI? I do not think so!

Thanks for all the helpful info. If the only way to get cheap outgoing calls to the U.S. from a number of countries is to use two phones, I'm up for it!

That's better!! You are now officially a phone geek / phone nerd! Welcome to the club!
:clap:

I have a special free voip did number that I use to trigger the callback.

I use a regular prepaid phone to make the call to that number. I receive a busytone and pbxes will call me back on my roaming free mobile. Than I get a dialtone.

In the beginning i was using caller id to trigger callback but depending on country different on no caller id were sent so sometimes I was unable to trigger a caller id.
For example using my dutch prepaid in holland it would sent caller id 06xxxx
when outside netherlands it could be 00316xxx or 316xxx
This meant settingup 3 caller id's to trigger a callback. pbxes only allows 3 so I could not use more. In case when outside nl the prepaid would not sent a caller id I could not trigger a callback.

So I endedup by getting a free voip did number. Anyone calling that number will trigger a callback to my roaming free cellphone. As I only know the number I never had a problem of someone else calling that number.