0873 numbers are categorized as "Special Services: Higher Rate" numbers.
They are not currently in operation and are reserved for future use.
They are in the same category as 0871 and 0872 numbers, so won't be included in free call bundles from telecoms providers, unlike 0870 numbers.
The cost of calling 0873 numbers will be in line with those of 0871 and 0872 numbers: currently up to 15p per minute from a landline, plus a call set-up fee, and up to 41p per minute from a mobile phone. The calling cost varies with the telecoms provider and the individual number.
0873 numbers cannot be described as 'national rate' numbers, and the Advertising Standards Authority can take action against companies that describe them as such.
0873 numbers, 0871 numbers, and 0872 numbers are regulated by PhonepayPlus.