cellphone use in Europe

Yes if in the UK you are using a UK phone, not in a way if you are using a US phone (but you will have roaming charges) but then your friends will be paying for an international roaming call from the US->UK as well, so they might not stay your friends when they get home to the bill. If you were elsewhere in Europe you would be roaming on a UK phone, and the effect of making intra-EU calls cheaper by regulation has pushed up the cost of phoning outside the EU.

You will all be charged for an international call unless you all buy phones with European carriers. For ATT it is 1.29 a minute. In my opinion, it is not worth it to buy an international plan unless you anticipate spending a lot of time on the phone. My family and I usually communicate through text when we are abroad and separate for the day. And only call in emergencies. This works very well. Using this method, my cell phone bill is an extra $10-$20 per week I am abroad.

Diane, There are a couple of different scenarios..... (1.) If you use your U.S. cellphone to call your friends U.S. number - You will pay for a long distance call to the states at your applicable international roaming rate, and your friends will pay for an incoming call at their applicable roaming rate.
(2.) If you use a phone bought in England to call your friends U.S. number - You will pay for an international call in accordance with the cellular plan that you chose at the time of purchase, and your friends will pay for an incoming call at their applicable roaming rate. The cheapest method will be to use text messaging. Normally the sender pays for an outgoing text and incoming texts are often free. However if you're both using U.S. based cell plans, the costs may vary according to the terms of the roaming plans of each of your cellular providers. Happy travels!

Thanks all for your help!

And, to complete Ken's post, if you both buy phones in England to call each other while in England, the caller pays for a domestic call, and the receiver pays nothing. However, calling a UK Mobile costs more than calling a UK land line (to make up for the fact that receiving calls on a UK mobile is free). Just like in the US, some providers have discount deals when you call another mobile on the same network. What this means: if you plan to make a lot of calls to your friends or vice versa, it may pay for both of you to get UK mobile phones (or UK SIM cards for your current phones, if they take SIM cards, if they have the correct bands and if they can be unlocked). Example, using approximate numbers: If you both take your US phones and you make a 2 minute call to your friend, you may each pay $3 (total cost $6). But if both had UK phones and you made that 2 minute call, you might pay £0.30 and your friend would pay £0 (total cost ~$0.50). That difference can add up fast if you're on the phone a lot. Of course, you have to figure in the cost of buying basic phones (probably about £20-30 each), and the time it will take to buy and set them up (a store like Carphone Warehouse will take care of setup when you buy it). Also note that when you take your UK phones to other European countries, you are roaming, so you will pay more, and receiving calls is no longer free. However, roaming costs are capped within the EU, and the caps keep getting lowered. Beware places like Turkey, Norway, Croatia, or Switzerland that are not EU, as costs can skyrocket. My friend has a T-Mobile UK plan with very good rates in the UK, for calling back to the US, and for use within the EU. He then checked the rate while roaming in Turkey - it was £1.50 per minute (ouch!)

Yes, you will be charged for an international call to call their U.S. number and they will be charged international roaming to call you. My personal feeling is that you can justify the cost of picking up a couple of cheap local cell phones pretty quickly. If the roaming charge for using a U.S. phone in the U.K. is $1.29 a minute (really a best case scenario), it won't take many calls before you've spent more than the roughly $25 you spent to buy the phone, sim card, charger, and some call time at an airport kiosk or downtown store. In Europe, you're local phone is only charged for outgoing calls - incoming calls are free. You can keep the phones for your next trip and just add a local SIM card, with time, at the airport.