Tara 03 numbers are not any more expensive to call then 01/02 . They are treated the same as 01/02 numbers for charging purposes by all UK Landline and Mobile Networks,and are included in inclusive minutes. No plans exists to change this as far as i am aware.They are therefore a perfectly good alternative number,and i cant see any compelling need to be specificially seeking alternatives to them.
"Ofcom introduced UK-wide 03 numbers as an alternative to chargeable 08 numbers, such as 0870.
These numbers allow organisations to have a single national point of contact without consumers having to pay extra to call them.
Calls to 03 numbers cost no more than a national rate call to an 01 or 02 number and must count towards any inclusive minutes in the same way as 01 and 02 calls.
These rules apply to calls from any type of line including mobile, BT, other fixed line or payphone "
http://ask.ofcom.org.uk/help/telephone/03number