01159 is not an area code in its own right. The area code is in fact 0115, and the following digit is part of the local number.
So 01159 should actually be written 0115 9, although it makes no difference when dialling the number.
For more information on 0115 numbers, see the page for the 0115 area code
The cost of calling an 0115 number
When calling from a landline, calls to 0115 numbers can cost up to 10p per minute, dependent on the time of day, and there is usually also a call set-up fee
When calling from mobile phones, calls to these numbers cost between 10p and 40p per minute.
Most landline operators offer inclusive call packages which allow calls free at certain times of the day, or at all times, and most mobile companies include free any-time minutes in the monthly contract payment, or a bundle of minutes for a reduced cost in the form of a top-up credit.