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I currently have only 700MB storage left on my free 5GB storage plan. I have both my iPad 2 and the iPhone 4 that syncs and backs up to iCloud. I was looking at the abailar storage plans for purchase and had a quick question. Let's say I bought the 10GB storage plan for $20 a year, but later decide I need or want even more storage, and later on buy the $40 a year plan....would I be able to only have to spend the extra $20 difference between the plans , or would I have I spend the $60 all together for both plans?