form validations

[eluser]Unknown[/eluser]
hello,

in my form i have 10 fields .
i know how to validate individually the validations. but i require how to validate either of one.


for example

in my form i hv the fields as firstname,lastname, username,password,email, phonenumber etc

if i want to place anyone of the email or phonenumber
i.e.,i want to enter either email or phonenumber only.


please help me.
thanq in advance