I did some digging on the Verizon web site and engaged in a chat with one of their representatives. The transcript is below. The cost is basically $5/month plus $1/minute for voice, $0.50 per text sent, $0.05 per text received, and $25/100MB data. Not too bad, and possibly worth avoiding the trouble of getting new cheap equipment at the terminal or in town, especially for just a couple days in France.
Ren: Hello, thank you for utilizing Verizon Wireless Online Chat channel! We are happy to have you as the most important part of the network. My name is Ren. How may I assist you with your contracted mobile service account today?
Randall: I will be traveling to Britain and France soon. Can I use my Droid RAZR MAXX phone there?
Ren: No worries, you can use it in England and France as well, Randall. All you need is to add the International Dialing feature to this phone and update the phone software before you leave the airport.
Randall: How much does that cost?
Ren: The feature itself does not cost anything. But the rate for calling in those two countries will be $1.29 per minute. And we have a value package you can add to the account to reduce the cost to $0.99 per minute.
Randall: What about the global voice plan I see on the Verizon web site that is $4.99 per month?
Ren: That's the one that reduce the minute rate for you, Randall. If you had that plan, the minute rate will be $0.99 per minute instead of $1.29.
Randall: OK. So for maximum savings, it's $4.99 per month plus $0.99 per minute, correct?
Ren: That's correct. But if you are only calling for less than 3 minutes, paying the roaming charge will be lower.
Randall: My wife, who will be traveling with me, has an iPhone 5, and we share the same bill. Will those charges cover her as well, or will the total charge for the two of us be double? And is the roaming charge in addition to the $4.99/month and $0.99/minute?
Ren: If you would like her phone to be able to make international calls, it will be an additional charge for $4.99 and also $0.99/minute.
Randall: OK. So if we are calling each other there the total will be $9.98/month and $1.98/minute. Are there any other fees, like roaming?
Ren: That's correct, it will be $9.98 per month plus the $1.98 per minute charge.
Randall: Please explain your comment: "But if you are only calling for less than 3 minutes, paying the roaming charge will be lower."
Ren: Oh, that's based on the $1.29 per minute charge. 3 minutes will be $3.87 in total for a month.
Randall: OK. What is the cost to for us to send and receive text messages to each other?
Ren: It will be $0.50 for sending one and $0.05 for receiving one, Randall.
Randall: What is the difference between the Global Data Plan and the "pay as you go" data rate?
Ren: The global data plan will be $25 for per 100 MB on data usage. And the pay as you go rate will be $20.48 per MB
Randall: If I get the global data plan, does the pay as you go rate even apply anymore?
Ren: Not at all, once the global data plan is applied to the account, the global data rate will be charged based on the plan. The "pay as you go" rate will not longer apply.
Randall: Since I am visiting two countries, will I need to sign up for the global data plan twice?
Ren: Not at all. That's the global plan for any foreign country you are traveling to, Randall.
Randall: Great. My wife and I share a data plan here in the US. Can we share the global data plan as well?
Ren: The global data plan is just like the global calling plan, it is only for one line.