I bought an unlocked sidekick but it shows me a activation scree, I can't do anything but receive calls

Press the top left button and "L" key at the same time to by-pass that screen and allow you to use the regular phone functions.

Let me start by saying I'm not an expert, but after going through a lot of gyrations I came up with a solution that worked for me. I'm sharing it here because I haven't seen a complete concise answer anywhere.
The activation problem with Sidekick Slides is common. Most of the time, people buy a Slide without realizing that you have to purchase a "sidekick plan" from T-Mobile to get it fully activated. These phones were build especially for T-Mobile, so they're designed so that you have to have a Sidekick rate plan first to get the phone activated. By the way, this applies to a new phone as well as a phone that's been activated before, but has been 'hard reset" (where you hold the R button while re-booting.. My advice, DON'T DO THIS! Because you have to re-activate the phone.
However, there's good news for all you non-T-mobile folks who bought a Slide on eBay (or from a friend etc.) only to find it needs activation. Here's the solution. If you search eBay for "sidekick activation" you can find folks selling prepaid activation kits for around $15. They include a sim card and about $10 worth of sidekick prepaid services. Buy the kit, install the sim, and go online to register your phone (registering by phone is a pain with T-Mobile). Online you have 3 plan choices: Pay By The Day, Pay As You Go, and Sidekick. Pick Sidekick, and then provide the requested registration information. When done, your phone should be ready to go and should activate within about 5 - 10 minutes. You'll be charged $1 a day and airtime for calls, so it's not cheap, but at least the phone won't go to the activation screen when you startup.
The next question is, how to unlock the phone for other networks? IF it's not unlocked you will be prompted for special code (this is different than the user-defined password that simply locks the phone against unauthorized users). It won't work on other networks until it's truly unlocked. Again, the trusty folks at eBay can help. I searched for Sidekick Slide Unlock Codes and found numerous vendors, ranging from $6 to $12, who provide permanent unlock codes for Slides. I found on that provides the code via email (others want to mail it to you) and got my code within 30 minutes. So now I can remove the T-mobile sim and put my ATT (or other) sim in and go. I should mention that some of the Sidekick features ONLY work if you have a sidekick plan, but that's T-Mobile's and Danger's devious attempt to make us miserable. Good Luck! Hope this helps! Rick

try pressing menu (the three bars) and L at the same time. i had an at&t sim card too and that worked.

hit menu and L

hi,hiba184 I think you press menu + L to make go away it worked for my sidekick slide

press the three line button and L @ the same

I have the same problem. But it says it could take up to 48 hours for the Welcome screen to appear. (Usually wouldn't take that long, usually it'll take about 1-3 hours)

I had the same problem when I bought my unlocked Sidekick.  Hold down the Menu and "L" buttons for about 5 seconds until the "waiting for activation" message goes away.

FLIP THE PHONE OPEN AND PRESS AND HOLD THE MENU KEY WHILE PRESSING L ON YOUR KEYPAD THIS SHOULD BY PASS THAT SCREEN...ENJOY

YOU CAN DO ANYTHING THAT IS POSSIBLE ON A UNLOCKED SIDEKICK


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