Ofcom rules in place since 2007 ensure that when called from within the UK, calls to 03 numbers are charged on the same basis as calls to 01 and 02 numbers. For the most part, calls to 01, 02 and 03 numbers are covered by inclusive call allowances. This also applies when roaming within the EU. If roaming further afield, calls to 03 numbers will be chargeable, but usually on the same basis as caling 01 and 02 numbers.

What is your issue with the 03 number? Is it an expectation of high cost such that you have postponed the call, or have you already tried to call and found yourself unable to get through? Where are you calling from? Is it a landline or a mobile? If a mobile, which country is the mobile number registered in?

Dave wrote on Mar 22^nd, 2018 at 11:31pm:

Yes, but what is the actual issue with the 03 number? Is it simply an expectation of high cost such that calling has been postponed, or has an attempt been made to call but was unable to get through? Where is the caller calling from? Is it from a landline or from a mobile? If a mobile, which country is the mobile number registered in? All these things could be useful in understanding the actual question.