0370 numbers are special phone numbers which are only used by certain businesses, government bodies and public sector organizations. Unlike regular phone numbers, they don’t have a geographical code number and hence they can be based anywhere in the UK.
This however doesn’t effect the cost of an 0370 number because all 03 numbers are charged at the same rate as standard calls regardless of the digits which follow them.
With TalkTalk the cost will depend on your plan. If you have the Plus TV/Plus plan than all 03 calls are included in your plan. If your on the Essentials TV/Essentials plan all 03 calls made between 7pm and 7am and on weekends will be included in your plan. At all other times and if your on any other plan then all 03 numbers will be charged at a rate of 13.5p per minute.