0870 and 0845 numbers have been inclusive from BT landlines only since 2009. They are inclusive only at the same time of day that 01 and 02 numbers are inclusive in your call package. At all other times you will be charged for the call.
Some of the other landline operators allow 0870 as inclusive calls, but not 0845 numbers.
0843, 0844, 0871 and 0872 numbers are never inclusive.
084 and 087 numbers (with the exception of 0870 from 2009 onwards) are all revenue share numbers.
Whenever you see an 084 or 087 number advertised, replace the 08 with 03 (keeping the rest of the digits the same as before) and see what you get. It will either be answered by the correct company or will lead to a "number not yet in service" error message. 034 and 037 numbers are reserved for the users of the matching 084 and 087 numbers.
If the 03 number doesn't work, then
http://www.saynoto0870.com/ might list an 01 or 02 number that you can ring instead. Recognising that some 08 numbers cannot be called from abroad, a number of companies advertise an alternative UK 01 or 02 number to call. Use this number or an 03 number whenever you can.
03 numbers were introduced in 2007. These are usable in inclusive minutes from landlines and from mobiles. If you have to pay for calling 03 numbers, (i.e. from pay as you go mobiles and from landlines without inclusive minutes) they cost exactly the same as 01 and 02 numbers.
Before 2005, 0870 was aligned to "national rate" and 0845 was aligned to "local rate". In 2005, landline operators scrapped the price differential for local and national calls, instead charging a single "geographic" rate for 01 and 02 numbers. They also introduced call packages with "inclusive" calls of up to one hour per call to all 01 and 02 numbers. At that point, "local rate" and "national rate" ceased to exist.
0845 and 0870 numbers, being chargable and non-inclusive, had overnight become expensive in comparison to calling 01 and 02 numbers. As they included a revenue-share element, "a premium", in the call price, they had in effect become "premium rate".
0844 and 0871 numbers have always been revenue share numbers and have never had any link with "local" or "national" call prices. These are never inclusive. 0843 and 0872 are newer and follow the same rules. Call prices for these from BT lines are capped. BT are not allowed to make profit on these calls.
Since 2009, 0845 and 0870 numbers are usable within "inclusive minutes" in BT packages. Ofcom removed revenue sharing from 0870 and made 0870 "inclusive" in 2009. BT expected Ofcom to remove revenue sharing from 0845 too. BT made 0845 "inclusive" but Ofcom didn't proceed with the expected changes. BT currently subsidises calls to 0845 numbers.
It's now 0843, 0844, 0871 and 0872 numbers that are the expensive ones from landlines. These are revenue share numbers. In comparison, most people can ring 01 and 02 numbers for up to one hour at no cost since call packages were introduced in the early 2000s.
Ofcom propose cleaning up the 084 and 087 number ranges. In 2013, several changes are expected:
- 0870 will return to revenue share and align with 0871 and 0872 revenue sharing numbers.
- 0845 and 0870 will no longer be inclusive calls from landlines.
- 0845 will align with 0844 and 0843 revenue sharing numbers.
- Price caps that apply to 084 and 087 numbers dialled from BT lines will be lifted.
- The Consumer Rights Directive will force many 084 and 087 users to move customer service and other similar functions to 03 numbers. This will benefit landline and mobile users alike.
- Users of 084 and 087 numbers will have to publish the revenue share that applies to their number (details
http://www.ofcom.org.uk/static/numbering/s8_code.txt of amounts) under the new "unbundled tariffs" proposals.
The history is quite complicated, and detailed here:
http://en.wikipedia.org/wiki/Non-geographic_telephone_numbers_in_the_United_Kingdom#History_of_non-geographic_prefixes