5.ac
Ambiguous Single Digit
Telephone Number Shorthand, Extension or Status Code

Telephone Extension 5
or
Status Code 5

5 by itself is ambiguous. ICUC thinks you might have entered an unknown telephone number shortcut abbreviation or a telephone number extension without a preceding telephone number or a status code without any telephone number to apply the status code to. To make use of telephone number shorthand abbreviations you must first perform a login from this device. After login, depending upon how you have set up your account, here are some valid ways to use a single .ac digit:

5.ac Ex: Access web site of recent telephone number who's last digit is 5
or
c.5.ac Ex: Calendar for last used telephone number ending in digit 5
or
e.5.ac Ex: Email last used telephone number ending in digit 5
or
i.5.ac Ex: Instant Message last used telephone number ending in digit 5
or
s.5.ac Ex: Get status of last used telephone number ending in digit 5
or
w.5.ac Ex: Access web site of recent telephone number who's last digit is 5
or
x.5.ac Ex: Access web site of recent telephone extension who's last digit is 5
or
800.555.1212.5.ac Ex: Access web site of telephone number 800.555.1212 extension 5
or
17.9797.800.555.1212.5.ac Ex: Set the status of telephone number 800.555.1212 x5 to status code 17 assuming that 9797 is a valid PIN code for performing status updates.

more information on telephone number shortcuts, extensions and status codes...