To call Canada or any of the 18 island territories in or near the Caribbean (including Bermuda, Bahamas, Jamaica, and Trinidad & Tobago) that share telephone country code +1, you just dial 1 + area code + number, the same way you dial a long-distance call within the United States.
To call other countries, dial the international access prefix 011, then the country code (a one-, two-, or three-digit number), the city code or area code (if any), and the subscriber number. If you have a GSM cell phone, you can replace the 011 prefix with the plus symbol (+).
Note that with many countries, you must drop the trunk prefix 0 from the beginning of the domestic number. For example, London's 020 becomes 011-44-20 and Melbourne's 03 becomes 011-61-3. However, the rule does not apply to all countries; for example, Rome's 06 becomes 011-39-06.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
It would be an international call, so yes you would have to pay in order to dial a number in the United Kingdom from the US.
Dial 011, the international access code. Dial 353, the Irish country code. Drop the 0 from the beginning of the city code. Dial the remaining digits.
To call this number from the US, dial the international dialing code (usually 011), followed by the country code, the area code, and then the phone number.
To call Singapore from the US, dial the international access code (011), followed by the country code for Singapore (65), and then the phone number you wish to reach.
To call Singapore from the US, dial the international access code (011), followed by Singapore's country code (65), and then the local phone number in Singapore.
The dial code for Australia is 61. To make an international call to Australia, you would need to dial your country's international dialing code, followed by Australia's dial code (61), and then the area code and phone number you wish to call.
Dial 0061 (the international access code for Australia) - then the number in full.
Dial 0061 (the international access code for Australia) - then the number in full.
To call from the US to an Australian mobile phone, dial 011 = international access prefix 61 = country code for Australia the Australian mobile number, omitting the leading 0 To call an Australian mobile that is roaming in the US, dial the Australian number as you normally would.
The telephone country code for North America (US, Canada, and several island nations and territories in or near the Caribbean) is +1. The plus sign means "insert your international access prefix here." The international access prefix from Cameroon is 00, so to call the US, dial 00 + 1 + area code + number. (To call from the US to Cameroon, dial 011 + 237 + number.)
If the US mobile phone is in international roaming mode, you may be able to dial its normal US number. If the phone has swapped in a UK SIM card, you will need to dial the UK number.
You will have to use the international operator to make that call.