Dear Google,

If an address book has a contact with both a home and work phone number, please indicate which number is which in the Messages app. I just sent a birthday message to my sister’s work phone by mistake.

Something like this would be enough:

A message exchange shows a birthday greeting followed by a response clarifying the use of a work number. This is annotated with a red box around the heading, which has a 'Work' badge underneath the contact name. A sticky note below it has the message: note the 'Work' indicator below the contact name.

Regards,

lmika