Luckily, there's this:
gtalk2voip
google it, stupid forums won't let me post the url, but it's that with a www and a .com
It's basically a cross-platform/protocol interchange, no software required, it just lets you use a windows live (or other IM address) as a sip address.
""2. Q: Ok, how can I call Google Talk, MSN or Yahoo users from SIP ?
* A: This is a major feature of our gateway and it is very easy. GTalk:
user@domain.com can be reached by calling to sip:user_at_domain.com@gtalk.gtalk2voip.com
* MSN:
user@domain.com can be reached by calling to sip:user_at_domain.com@msn.gtalk2voip.com
* Yahoo:
user@yahoo.com can be reached by calling to sip:user_at_yahoo.com@yahoo.gtalk2voip.com
* AIMi/iChat:
screenname@aim.com can be reached by calling to sip:screenname_at_aim.com@aim.gtalk2voip.com
* ICQ:
screenname@icq.com can be reached by calling to sip:screenname_at_icq.com@icq.gtalk2voip.com ""
make sure you actually type the _at_, as two @s won't work.
so if your recipients msn address is
mickeymouse@hotmail.com, you call
sip:mickeymouse_at_hotmail.com@msn.gtalk2voip.com from ekiga
then they simply accept a contact that auto-adds them and you should be good to go.
the service can also leave voicemail messages in their email inbox, free of charge.
personally, unless the person I'm trying to contact is not very comfortable with computers, I would simply install ekiga on their pc, especially seeing as they have a windows client now.
good luck