It is possible to call London from anywhere in the United States. While dialing an overseas destination is different than making a domestic call, it is not complicated.
To place a call to the United Kingdom from anywhere in the United States, dial 011, the exit code for any call from the United States to anywhere in the world. Then, dial 44, the country code for the United Kingdom. Every country in the world has a unique country code.
If calling a landline, enter the area code and then the local number that totals ten digits. If dialing a mobile phone, there is no area code but there are still ten digits. For instance, if calling a mobile phone in London, a sample number might be 011 44 1234567890.