but (1) now I want to add this field in everywhere like one-page checkout, order page, sales page, shipping page, invoice detail page..likewise...so it is possible in my one custom module?? (2) or should I create this functionality in one module or i have to create the different module for each other any help should be appreciable?
You can add this field everywhere it's needed (as you mentioned checkout, order page, sales page,...) etc. within one module.
A module named
Vendor_MobileNumber or even better
Vendor_CustomFields (or similar) (where
Vendor is your vendor/company name) could be handy so that you can extend it later for additional fields.