use a regular expression validator with the expression:
[+0-9]{13,}
this will allow characters + and 0 to 9 with a minimum of 13 (+3 because of the +91)
hth
ps, if it doesnt work play around with it a bit, but on top of my head this should do it...
hth
please mark answers as Answered and please post back solutions when you figure stuff out.
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