How can change telephone field from 'Telephone' to only 'Mobile Number' in magento

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• app/locale/en_US/Mage_Checkout.csv
• app/locale/en_US/Mage_Customer.csv
• app/locale/en_US/Mage_Persistent.csv
• Where en_US is your current locale.

Find the following line “Telephone”,”Telephone” and change the second part to your “Telephone”,”Mobile Number”