Yes, calls to 03 numbers may be 'inclusive' but they are never 'free'.
Calls to 01, 02 and 03 numbers are chargeable. You either pay a monthly fee for a package of inclusive calls or you pay a (usually very high) per-minute rate.
Inclusive call plans are available on landlines and on mobiles. On landlines, there's a choice between 'Weekend', 'Evening and Weekend' or 'Anytime' allowances. On mobiles, inclusive allowances are available both in the form of a contract or as a pay-as-you-go add-on or bundle.
Calls that are 'free' are to numbers starting 080 and 116 and numbers such as 105, 111, 112 and 999.
This explains the differences between 03 numbers and the various 08 numbers:
https://www.nidirect.gov.uk/articles/contacting-08-and-03-numbers