use ::helper::*;
use ::Fake;

pub trait PhoneNumber {
    fn phone_number() -> String;
    fn phone_number_with_format<S: AsRef<str>>(format: S) -> String;
    fn cell_number() -> String;
}

impl<T: Fake> PhoneNumber for T {
    #[inline]
    default fn phone_number() -> String {
        let len = T::PHONE_NUMBER_FORMAT.len();
        let number_format = T::PHONE_NUMBER_FORMAT[gen_range(0, len)];
        numerify_sym(number_format)
    }

    #[inline]
    default fn phone_number_with_format<S: AsRef<str>>(format: S) -> String {
        numerify_sym(format.as_ref())
    }

    #[inline]
    default fn cell_number() -> String {
        let len = T::PHONE_CELL_NUMBER_FORMAT.len();
        let number_format = T::PHONE_CELL_NUMBER_FORMAT[gen_range(0, len)];
        numerify_sym(number_format)
    }
}

use ::helper::*;
use ::Fake;

pub trait PhoneNumber {
    fn phone_number() -> String;
    fn phone_number_with_format<S: Into<String>>(format: S) -> String;
    fn cell_number() -> String;
}

impl<T: Fake> PhoneNumber for T {
    #[inline]
    default fn phone_number() -> String {
        let len = T::PHONE_NUMBER_FORMAT.len();
        let number_format = T::PHONE_NUMBER_FORMAT[gen_range(0, len)];
        numerify_sym(number_format)
    }

    #[inline]
    default fn phone_number_with_format<S: Into<String>>(format: S) -> String {
        numerify_sym(format.into().as_str())
    }

    #[inline]
    default fn cell_number() -> String {
        let len = T::PHONE_CELL_NUMBER_FORMAT.len();
        let number_format = T::PHONE_CELL_NUMBER_FORMAT[gen_range(0, len)];
        numerify_sym(number_format)
    }
}

--- 
+++ 
@@ -3,7 +3,7 @@
 
 pub trait PhoneNumber {
     fn phone_number() -> String;
-    fn phone_number_with_format<S: Into<String>>(format: S) -> String;
+    fn phone_number_with_format<S: AsRef<str>>(format: S) -> String;
     fn cell_number() -> String;
 }
 
@@ -16,8 +16,8 @@
     }
 
     #[inline]
-    default fn phone_number_with_format<S: Into<String>>(format: S) -> String {
-        numerify_sym(format.into().as_str())
+    default fn phone_number_with_format<S: AsRef<str>>(format: S) -> String {
+        numerify_sym(format.as_ref())
     }
 
     #[inline]
Use ´AsRef<str>` instead of `Into<String>`

Avoids unused allocations
