Make sure whosoever phone numbers are given their phone is on in the
preceding couple of days 24x7
and they have help of 2-3 people so
connectivity is there because people are going to be calling if they
are stuck somewhere or the other. If you have more than 1 the
possibility of reaching you (as the institution is much more). You'll
probably may even get calls at all unearthly times so somebody should
be always their to guide them even if you can't reach them. When
somebody reaches an unknown place, even if s/he hears a friendly voice
lot of the anxiety, confusion etc. clear up. Whether they are
co-ordinator or helper or whatever, name and numbers for emergency
or/and guidance should be there.
Make sure they understand the role.
Also be up-front if it's going to take time to receive them or
something or if you are unable to come and they have to make their own
way. Either way, be upfront about your situation, it would help to
have things smooth for the unconference as a whole.