Contacts validation: email or telephone should be entered

Hi all,

I have this simple requirement to ensure that when saving Contacts, either the email or the telephone should have a value.  If both are blank, issue an error message.

I am using SAP CLoud APplications Studio.  I have created an extension of the BusinessPartner BO but I understand that this may contain not only Contacts but others like Sold-To , etc.

In Validation:OnSave logic:

1) How can I check that it is only validating Contacts and not other business partners?

2) How do I access the current values of Email and Telephone fields of the QC screen?  I tried

this.AddressInformation.AddressSnapshot.Email or Telephone

or

this.BusinessPartnerRelationship.ContactPerson.ContactWorkplaceAddressInformation.AddressSnapshot.Email or Telephone

but the above have no Content in dropdown (only Count, GetFirst, etc., which still gets invalid syntax message).

3) Are the Email and Telephone fields allowed to have multiple entries?

Sorry, still a newbie to this.  Hope anyone of you can help me.

Many thanks.