I found this. I haven't verified this but hope it helps! It appears the K800i cannot be unlocked by free downloadable software
REMOTE UNLOCK your Sony Ericsson Mobile Phone(s)
Support SE K800i k800 K800i W880 W880i W850
--No need to send your valuable SE mobile phone(s) to phone shops and being returned if they cannot unlock it, waste time!
--Able to use other networks and oversea.
--Unlock your mobile phone at home by using the datacable only
IMPORTANT: Please read below :
Our software can only support CID 49 and CID51 Sony Ericsson k800 K800i W880 W880i W850 only, belows is the software for you to test your phone CID number by using the datacable, so DO NOT BUY BEFORE YOU KNOW WHAT IS YOUR Sony Ericsson phone 's CID number
Download the following program:
www.kingmobilephone.com/cidcheck.zip
Then, unzip the files and read the instruction in the folder. The file is called “instruction.txt”
SE recently implemented a new protection called CID52 which our software cannot unlock it. However, most SE phones in the market are with older protection such as CID51 or 49, so if your phone is NOT with CID52, then YES, you can use this D.I. Y unlock package and unlock your phone at home.
Belows is a screenshot to show you how to read the CID number:
http://www.kingmobilephone.com/shot.JPG
This D.I.Y. unlock package includes:
(1) ONE unlock credit which allows you to unlock ONE SE phone. (Discount on buying more)
(2) Clear step by step instructions of how to UNLOCK your Sony Ericssion Phones as mentioned above
(3) This D.I.Y. package will remove all the horrible service providers branding, it will put back the Sony Ericsson generic software for you. Of course, it won't have this effect if your phone already got the generic firmware.
Cost is £16 included unlock & debrand remotely.
Payment can be made via paypal / Nochex / Credit card
Also, instructions will be sent to your paypal email address unless you give us another email address.
contact us at MSN / Email at
yingsquare@yahoo.com