I won't try to sell, I won't over-promise but I will give straight answers.
Calls to 0203 numbers are normally charged the basic or local rate.
Calls from landlines are typically charged up to 16p per minute. Some providers charge a 23p call set-up fee but this can vary. Most providers offer call packages that allow calls free of charge at certain times of the day.
Call costs from mobiles vary according to the calling plan chosen.