I don't really know that much about upgrading phones so could anybody explain to me if I could upgrade my sidekick slide to a sidekick 2008 and if it would cost me anything
Sidekicks are never free, so it would certainly cost something. You probably can upgrade at a discount, if you have a contract account and extend the contract; just log in to your My T-Mobile account to find the Upgrade link (it's under Shop on the left) and this will let you know the discount you get on any of the phones T-Mobile has now.
Some types of accounts (FlexPay mostly) can't upgrade online, and then you need to call 611 or go to a store to upgrade or check your pricing.
Most likely I'd guess you're eligible for a partial discount as you probably either opened your account or upgraded since last fall, so it's probably around $199.99. There's also an upgrade fee that's $18.
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Sidekicks are never free, so it would certainly cost something. You probably can upgrade at a discount, if you have a contract account and extend the contract; just log in to your My T-Mobile account to find the Upgrade link (it's under Shop on the left) and this will let you know the discount you get on any of the phones T-Mobile has now.
Some types of accounts (FlexPay mostly) can't upgrade online, and then you need to call 611 or go to a store to upgrade or check your pricing.
Most likely I'd guess you're eligible for a partial discount as you probably either opened your account or upgraded since last fall, so it's probably around $199.99. There's also an upgrade fee that's $18.