And here's a longer answer:
Calls from a mobile will always cost more, unless they are to a regular mobile on the same mobile network, or to a number that has been set up for mobiles (and includes your network).
Premium rate numbers start with 09xx (formerly 0898) in the UK, and 15xx in Ireland. You cannot call any country's premium rate services from outside that country (as far as I am aware), and abuse is watched for very closely by the phone companies and service providers involved.
The per-minute cost is divided up between the phone companies, service providers, and operators.
They don't work from phone boxes or over prepaid calling cards.
Ireland's 15xx prefixes usually have more charged per-minute the higher the 3rd digit is, and 1559 is dedicated to sex lines.
As an alternative to national premium rate numbers (which would require one number to be set up per country), most of the "TV Babe" channels use an international number (starts with 00), and show it on screen as being for callers from Ireland. Most of them use country codes for small islands in the South Pacific, where a tiny local population allows for very short numbers, so even with all the codes in front, it doesn't look too obvious on a phone bill (until you see the price and the distant country that is).
There have been cases of island locals getting strange phone calls at all hours and complaining, but for a very small population, their link to the rest of the world is being subsidised by the profits from all the calls that aren't wrong numbers.
Unfortunately, due to widespread abuse by computer virus "dialers", most of these country codes have been blocked across the board by Eircom, and you have to ask Eircom (or your phone company) to unblock them before you can call them. So either you have a mate living in Fiji, or you are a perv
Country codes are in the front of the phone book, and rates are listed on the back of your bill.
There's more info here:
http://en.wikipedia.org/wiki/Premium_rate
The bit at the bottom about international calls is interesting: it implies that the calls don't always go halfway around the world (you just get billed as if they did).