Hi, yes 03 numbers are the same rate as 01 and 02 numbers (UK Geographic numbers). The idea of 03 numbers was for organisations and businesses to offer a National number charged at Geographical rates because the EU introduced a law that Customer services and other support helplines could no longer charge a premium and have revenue share which is why most businesses moved from 0843,0844,0845,0871,0872 and 0873 numbers to 03 numbers.
Because calls to 0800/0808 numbers were chargeable from mobiles, many companies set up a 03 number alongside the freephone numbers, however, Ofcom rules requires that all service providers whether they are landlines or mobiles are not allowed to charge for Freephone numbers (0800 and 0808) from 1st July 2015
With BT calling plans, you can make up to 150 calls each month or not exceeding 1,000 minutes per month to call 0845 and 0870 numbers. This does not include 0843,0844,0871,0872 or 0873 numbers and you will be charged a service charge per minute and access charge per minute, so for example the Access charge per minute from a BT Mobile phone is 31.2p per minute and then the service charge would be the advertised rate of the 08 number for example 0844 8p per minute so you'd add 31.2p + 8p per minutes so it would be 39p per minute in total.