Depreciation

JUST ADD 3000 IN ADDITIONS COLUMN LESS/MORE THAN 180 DAYS AS PER DATE OF EXCHANGE

But the cost of the new mobile is just Rs.9000/- as per bill...

AS PER WDV CONCEPT COA OF NE ASSET IS 3000

i didn't got u r question, if u want to say u exchanged by paying 3000 then following entry should be passed

new Mobile ( cell phone) .........................Dr    9000

Profit And Loss A/c.....................................Dr    6000

            To Bank A/c                                                           3000

             To Old Mobile A/c                                               12000

if u exchanged without paying anything then

new Mobile ( cell phone) .........................Dr    9000

Profit And Loss A/c.....................................Dr    3000

            To Old Mobile A/c                                               12000

can u please elaborate u r question

pls give more details of your question otherwise ans of evry 1 will be based on assumptions.

Give more factual data.