Skype while traveling
Use Skype (and an internet connection) to make and receive free voice and video calls—or have your friends and family Skype your cell in the U.K. for 10¢ per minute or $1–$2 per month.
No matter if you rent a cellphone, buy a world phone, or carry your own phone, convince your friends and family to save a bundle by not calling you on it but rather by Skyping you.
Just have friends and family back home call you on your new phone using Skype, which will cost them a mere $2 per month for a flat rate to the U.K., or 10¢ per minute for pay-as-you-go.
(Yes, Skype is normally just 2.3¢ per minute, but that's for calls to land lines; calls to cellular networks cost a bit more...though still usually less than a regular phone line, calling card, or international dialing plan).
Even better, connect to the internet via an internaitonal roaming plan—or, preferably and more cheaply, the hotel's or public WiFi—and use Skype yourself to make free Skype-to-Skype calls—even video calls for free.
Sure, the voice quality is not pristine. It usuually sounds a bit digitally compressed, and sometimes you get a pop or skip—but since it is free (or practically so), who's complaining?