Call the USA (country code 1)
for 1p/minute:
0844 720 8155
Use it for both landlines
and mobiles in the USA.
Dial 00 + country code + tel. number without the first zero.
For example, for the number
08 - 44 55 66 in Sweden
(country code 46),
you would dial: 00-46-8-44 55 66