FM to change contact person relationship data is 'BAPI_BUPR_CONTP_ADDR_CHANGE'
There is following step to maintain the mobile number and telephone number of contact person relationship.
1. Maintain the BAPIADTEL with these values telphone number eq number(04586456454) ,country code eq (US) and in, R_3_user parameter eq ( 3 for mobile and 01 for telphone number) and Consumer eq 002.
2. Maintain the BAPIADTTX with value X. if there is one telphone number and one mobile number then there should be two entries.
This will help you.