The 118 499 charity directory enquiries service, which donates 5p from every call to the British Red Cross and Barnardo's, has turned to direct mail and TV advertising to raise its profile.
Operator Share Communications recently included a mailout with stickers in the two charities' member magazines, and tested TV campaigns on ITV Meridian and Sky.
The number has now received more than 500,000 calls and raised more than £30,000 for the charities since its launch last August, but still has less than 1 per cent of the total directory enquiries market.
It was given a top customer satisfaction rating in a Which? survey last year.
Share Communications says the service is on average 21 per cent cheaper than major rival services 118 118 and 10 per cent cheaper than BT's 118 500.
Managing director Steve Warner said: "If one in five calls to directory enquires were to 118 499 it would raise £1m for each charity."