Here is some hard-earned wisdom:
 

TAKE TWO! ONE WILL BE BETTER.

Piranha is a good choice. You do not mention what phone you have.
Having a second/different SIM will provide some hopefully failsafe protection if you need to be more sure of your ability to call out. A dualSIM phone makes that second SIM more practical and easier to use.

I have and plan to use an iPhone4. Although it doesn't seem to support seamless callback all providers give you the USSD to use to make a call. It's a pain but something I can live with. Maybe there's an APP that will take a number from my phonebook and prepend and append the necessary strings to the number to be dialed. I know there are options to make an iPhone take a dual sim but that's too much for my use case.

It all depends on where you are roaming and where you are based. For your case (US based) Piranha I think is best choice for you.
Even for Europe roaming from US customers I don't recommend Toggle (except for heavy users), short exparation of the credit , plus 25UKpounds minimum topup .
Even if US customers roam in Europe, I suggest Piranha or EVRIKA (Chezh republic +4207910) with very low termination rate to their numbers ($0.02 to $0.03/minute)..so you can forward a US DID number to their +4207910 via a voip provider (eg zadarma,, telecallmart, etc) with a very low connecting cost and free incoming calls to the simcard to all european countries, including SWitzerland, Turkey, Russia. Plus free incoming calls to some other non-european countries as China, Australia, SouthAfrica etc)

For data only US customers roaming in Europe I strongly suggest https://gigsky.com with excellent prepaid plans on all European countries of
$25.00 175 MB 7 Days
$35.00 300 MB 14 Days
$50.00 500 MB 30 Days

But if small data sessions is the case, Piranha new data rates of $0,15/mb in most Euporean countries is a good alternative

For very heavy data roaming users in Europe I suggest a Vodafone Italy prepaid simcard bought here http://www.mobipassport.com.au/Vodaf...-p/voda-eu.htm or here: http://www.europasim.com/epages/6335...ops%2F63355149 (same product)

with €3 per day you get all round Europe:

500MB Internet (Speed reduced after first 500MB)
50 SMS (Additional SMS is €0.11/SMS)
25 min Outbound calls within EU (Additional usage €0.35/min)
25 min inbound calls within EU (additional usage €0.10/min)

Piranha is more expensive for calls & sms + they charge for incoming calls. This is absolutely not interesting compared to Toggle in the Toggle countries.

Furthermore, min reload is not 25 £ but 20£, which gives you 20£ + 10% = 22£ credit.

Credit NEVER expires as long as you are using your SIM at least once every 4 months (call, sms or data charge). This means, if you want to be an extreme saver, that you never have to recharge your SIM as long as you have enough credit for this (ex: 1 data charge of 0.0002 every 4 months).

Really, if you are making so little use of the SIM that a 20£ reload is too much, then I can't see how it would make sense to go through the trouble of ordering a roaming SIM. Just use your normal T-Mobile or AT&T plan for those few minutes you need.

That said, of course if other non-toggle countries are part of your journey, other SIMS like Piranha should be taken into account.

the best callback voip provider at the moment is: http://www.callimax.com/
great rates with per second billing

manual callback works great. tested for several months.
android app not working, haven't used iphone app to comment

Thank you both. I appreciate your opinions, recommendations and information.

Hi hwa, not sure of what your travel plans are, if its to the Winter Olympics Piranha have just posted on there F&Qs. Rates look good. Anybody know if you are allowed to buy local.

" Piranha adds new network, (Rostelecom) which covers the Sochi area of Russia. Direct dial with very competitive roaming Data and SMS rates."

There are two camps you see on this forum with respect to incoming calling rates. The first group wouldn't care if the roaming SIM provider gave you a country code 8816 prefix (iridium satellite phone) if the calls were free to them. "If you want to call me when I am out of the country, that's your problem."

The second camp, wants to absorb the cost that the caller would pay and is looking for the cheapest way to make the roaming call a local call for their caller. Those folks assume they will be paying something to forward the calls.

Many of us have also had several roaming SIMs go belly up in the past and are sensitive of pricing structures that are "too good to be true." While we are cost aware, we shy away from the operating who offers free incoming calls on cruise ships. They simply won't be around very long. If I am going on a trip and looking for a solution for only that trip, I'd probably gamble, but I am also prepared to spend a little bit more roaming for a little more stability.

I sent a friend on a trip with one of my SIMs and the carrier ceased operations while she was out of the country. Trust me this was the least technical friend I have. Bad idea!

Good observation and synthesis.
Outside this forum are more camps.
1. Those who don't know international SIM cards exist.
2. Those who see one advertisement for an international SIM card and buy it.
3. Other states of confusion.

Don't forget, since you are a U.S. person, if you get T-Mobile service- unlimited texts and data (at about Edge speeds) and 20¢ calling (in and out) in 100+ countries.