connection problems between a specific landline and a mobile phone?

my friend has samsing sgh b130 mobile phone. When I ring the phone from my landline, I hear two ring tones and then am transferred to his voicemail. at his end the phone does not ring. However if I ring his mobile from another landline or a mobile phone then the phone rings at his end, His phone is on the orange network, we have contacted orange who say the problem is not with them, the landline has been checked and is ok, we contacted samsung, who thought that my number might be in his mobile 'reject call' list so we followed the advice, but he had no rejected numbers on the phone. Have you any idea what might be causing the problem and what the solution might be.