Multiple text message numbers for single contact?

[akates]

I am new to the diamond and for some reason I can't have multiple numbers available to text message to for a single contact. It seems that only the mobile number gives the availability to text directly when you click on a contact and I can't put in more than one mobile number for each person. Any workaround for this? If I hold down a non-mobile number it lets me send a text from there but I don't get why it won't then show up in the list next time I select that contact?