We don't want to support only 'relative' validity, so don't assume that the Validity property will always be a uint32 value. Instead, we define the Validity propery as '(uv)' tuple, where the first value (a MMSmsValidityType) specifies the type of validity, and the second value is a variant formatted accordingly to what the validity type specifies (e.g. a uint32 value if the type is MM_SMS_VALIDITY_TYPE_RELATIVE).