OK after few days of "investigation" into functional programming, i manage to code the following, which do the same job as my codes in question:
(define load-mobile-plan
(lambda (file)
(let [(mobile-plan '())]
(read-file file mobile-plan))))
(define read-file
(lambda (file mobile-plan)
(let [(line (read-line file))]
(if [eof-object? line]mobile-plan
(let* [(temp-pair (cons (string-normalize-spaces line)
(string-normalize-spaces (read-line file))))
(mobile-plan (cons temp-pair mobile-plan))]
(read-file file mobile-plan))))))
(call-with-input-file "xxx.txt" load-mobile-plan)