IPhone :: Using Contacts Phone Numbers While Traveling In Europe?

My wife and I own iPhone 4S phones and will be traveling with them to England for the first time this coming holiday season. We have Verizon service with international calling enabled, and intend to use Verizon's international calling plan for the period while we are to be traveling (no swapping for European telco SIM cards). We each have extensive Contacts lists in our phones, and both are synced to our Address Books on our home iMacs. We have our US contacts memorized in the standard area code + number format, and similarly we have our Brit friends' cell and home phone numbers memorized in the "011" (US exit code) "44" (England country code) + number format. With that we can of course call US numbers as normal and the Brits just fine while here in the US. But when we are overseas I suspect we would need a different number sequence to connect with family back here in the US if needed, and we certainly couldn't call the English phone numbers from within England using the 011-44 prefix before their numbers. Is there anyway to prepare for that situation short of re-entering a bunch of phone numbers for while we are away, and then changing it all back again when we return a few weeks later? How do people who travel overseas frequently, say on business, handle this? Multiple numbers in different formats for each Contact?

Info:
iPhone 4S, iOS 5.1.1