Retrieving ld voice mail from iPhone 4

I upgraded from my iPhone 4 to an iPhone 5 almost 2 years ago, then upgraded from the 5 to the 6 earlier this year. I still have my old iPhone 4, and there are some old voice mails on it from my father (who has since passed away) that I'd like to have on my iPhone 6. Actually I thought they were on my iPhone 6 ... but I recently learned they are not. I pulled my old iPhone 4 out and am charging it up now ... I looked at the voice mails and they appear to still be there. Is there any way I can get them to my iPhone 6?