On the topic of preferred contact method, the shift over the past four generations has been stark. (lawyermarketing.com)
If an employer would like to contact your references, provide their names and preferred contact methods upon request. (resume-now.com)
Such buckets may include preferred contact method (some references shine best via the written word, others flourish over the phone), relevant projects you may have done together and / or how well they can vouch for your specific skills or strengths. (theladders.com)