Hi My Motorola cordless phone C1012LX .In on of the handset it says unregistered .how to fix this problem.

SOURCE: AT&T 2230 2.4 GHz Dual Handset Cordless Phone - additional phones?

Hi yes you can add additional phones to it as long as their the same frequency so that they pick up the signal from the main phone that plugs into the phone line.
Im sure you can have upto 4 handsets but just make sure theis same make and frequency

SOURCE: handset says unregistered

The manual says that to register it needs to be completely powered off and then restarted. I unplugged my battery and then plugged it bacdk up.

SOURCE: GE MODEL 28112 DECT 6.0 CORDLESS PHONE

I contacted GE today and they told me how to get the caller ID to work on the additional handsets. You must follow these steps in the exact order given.

#1 - unplug the base phone
#2 - unplug the telephone line from the base phone
#3 - remove the battery packs from the phones
#4 - wait 10 minutes.

reverse the order when assembling. Put battery packs in phones, put the telephone line back in the base phone and lastly plug all phones back in. It takes about another 10 minutes after that before all phones start recognizing caller ID but it now works fine.

SOURCE: Deregister lost or broken phones

Some tricks from a helpful Uniden rep:

holding down end+# keys at the same time on the phone for about 10 secs (you will hear a beep) will deregister the handset. If you have a dead handset and want to deregister it from the base, you have to reset the base. unplug the phoneline and power. hold down the "delete message" key, plug power back in. about 10 secs later, you will hear a long beep (theres a short beep upon powerup as well). At this point all handsets are deregistred and you will have to reregister them with the end+# trick. this way when #1 handset is dead, you can make a working one #1 and get the broken one fixed

BTW, this is a woot warranty, not uniden warranty. however the uniden rep gave me the number to the people who refurb (rox0rz!) these. I'll post an update when I finally get ahold of them (and the number if its actually helpful)

SOURCE: The screen on the cordless

I think you may need to change the display