Inactive sim every time i turn my phone on it keeps saying inactive sim what shall i do my phone is a sony ericson k800i

There could be two reasons :
1) your sim card is inactive
2) the was reported lost/stolen and is blacklisted

Try changing another SIM card to test it. Place the SIM inside your phone in such a way that the SIM terminals comes into contact with the terminals present in the terminal.

1st switch on your phone without sim card and goto network settings and change the operation mode to GSM/GPRS 900/1800/1900 and switch off the phone and now insert the sim card and on it works

boss its simple.. please provide us ur IMEI no. of the phone.. we shall be glad to help u... cheers!!!

I assume you did not purchase the phone from a eputable source. The inactive sim message appears in this way when a person reports a sony ericsson phone lost or stolen. The IMEI number (unique to every handset) is used to disable functions of the sim reader.

hi Naidoo.
not sure if this forum will help you out but have a look.
K800i inactive sim
plus found this on the internet.

it may be the software needs reloading, if you download the "sony ericsson pc companion" to your pc you can connect your 800i by usb lead, then click on the companion panel for updates, it will give you the option to repair phone, select this option and all your software will be renewed. or if you prefer to contact orange first just go onto their website and the phone numbers will be there.
(AND THIS)

U just istall p.c. suit of sonyerricsson and take backup of ur data,, then u need to flash ur handset from sony erricson service centre.

OR THIS MIGHT HELP.
sony ericsson k800i inactive sim problem Google Search

I have the same problem since I got O2 to block my phone when i lost it. Now it's found it says "Inactive SIM", even though the SIM works in other phones.

you gotta wait for your provider to activate it if nothing it 2 days call them with your dilemma

contact ur service provider to chk abt si registry or sim validity....if it is all fine then change the n/w settings in ur fone and after that reinsert sim,,,,any issues pls go to care centre for chking of sim slots....