Invite to calendar greyed out for all contacts?

[Risco]

For some reason on my girlfriends phone contacts are greyed out when inviting to share calendar.

I am on iPhone as well. I can invite her, but even people with iPhones are all greyed out on her contacts. Why is this?

 

[posguy99]

For some reason on my girlfriends phone contacts are greyed out when inviting to share calendar.

Do these people have anything other than a telephone number listed in their Contacts entry?