Depreciation Schedule for Asset Purchases Throughout Year

I need to make a depreciation schedule for assets that are purchased throughout the year. Attached is a sample schedule for purchases of telephone systems.

Column C is where I want to input the cost of the asset and when the asset was purchased. I then want to depreciate the asset starting on the purchase month (all assets are expected to be fully depreciated in 48 months).

Right now, I'm inputting the purchase amount and period and then manually going to the appropriate column and starting my depreciation there. Obviously this is quite inefficient if I have multiple assets and purchase months; I was wondering if anyone can figure out a formula to automate this process so I can just input the amount and month of purchase and have depreciation go to the appropriate columns. Any help would be greatly appreciated.

Thanks!