US Dialling Prefix

[Jel]

I'm trying to ring Yahoo on this # (866) 924-6676 but my phone provider gives an automated message that the # isn't recognised, I assume because I need an extra prefix. After googling and being even more bamboozled, and ringing my phone provider who I kid you not gives this automated message (in the slowest speech speed possible):

Thankyou for ringing BT, please enter the number you are calling ABOUT (I automatically swear in frustration)

*enter number*

Sorry, this is not recognised, please hold.

Please select one of the following options
1. For billing enquiries press 1
2. If you are moving home press 2
3. For internet enquiries, including BT Broadband press 3
4. For other enquiries press 4

*presses 4*

Please select one of the following options

(More swearing, wife tells me to shut up)

1. For business enquiries press 1
2. To report nuisance calls press 2
3. To report a line fault press 3
4. For all other enquiries press 4

*presses 4*

Please select one of the following options

(More swearing, more extreme words, more wife telling me to shut up)

1. For internet enquiries press 1
2. For all other enquiries press 4

*presses 4*

sound of connection, followed by 3 double rings, followed by message:

Our operatives are on call from 8 am to 8 pm ( F word, C word, couple of B words, more F's and liberal amount of C's) Monday to Friday and (Hang up and swear more)

Holy fuck, it's 8.14 pm where I am

Aaaaaaaargh!

So, anyone able to inform me what prefix I need to call a US number?

Thanks