Greeting was somehow erased

Unfortunately the news is not good. The answering machine does not have tape storage. Everything is stored on a memory chip. Anytime you re-record the incoming call greeting, you overwrite the previous greeting. Sorry.

Call your KX-TM150B answer machine, it will answer after 15 rings if it has power but the answer function is turned off. The greeting will play and the answer function will turn on. I have included a link where you can download the manual.

http://service.us.panasonic.com/OPERMANPDF/KXTM150B.PDF

Greeting message
When the unit answers a call, callers are
greeted by a greeting message. You can
record your own greeting message or
use a pre-recorded greeting message.
Recording your greeting
message
You can record your own greeting
message (2 minutes max.).
1 {GREETING REC}
2 Within 10 seconds, press
{GREETING REC} again.
3 After the base unit beeps, speak
clearly about 20 cm (8 inches) away
from the MIC.
4 Press {?} (STOP) to stop recording.
Using a pre-recorded greeting
message
If you erase or do not record your own
greeting message, the unit plays a prerecorded
greeting message for callers
and asks them to leave messages. If the
message recording time (page 39) is set
to “Greeting only”, caller messages
are not recorded and the unit plays a
different pre-recorded greeting message
asking callers to call again.
Playing back the greeting
message
Press {GREETING CHECK}.
Erasing your greeting
message
If you erase your own greeting message,
the unit plays a pre-recorded greeting
message for callers.
Press {GREETING CHECK}, and then
press {ERASE} while your greeting
message is playing.
Listening to messages
using the base unit
When new messages have been
recorded, the message indicator on the
base unit flashes.
Press {6}.
L If new messages have been recorded,
the base unit plays back new
messages.
L If there are no new messages, the
base unit plays back all messages.
Operating the answering
system
Key Operation
{^} or {V} Adjust the speaker
volume
{7} Repeat message
(during playback)*1
{8} Skip message
(during playback)
{?}
(STOP)
Pause message
– To resume playback,
press {6}.
– To stop playback
completely, press
{?} (STOP) again.
{ERASE} Erase currently playing
message
*1 If pressed within the first 5 seconds of
a message, the previous message is
played.

check if this works and tell me if any issues

Greeting message
When the unit answers a call, callers
are greeted by a greeting message. You
can record your own greeting message
or use a prerecorded greeting
message.
Recording your greeting
message
You can record your own greeting
message (max. 2 minutes and 30
seconds). If you do not record a
greeting message, a prerecorded
greeting message is used.
1 {MENU}
2 {V}/{^}: “Answering device” i
{OK}
3 {V}/{^}: “Record greeting” i
{OK}
4 After the handset beeps, speak
clearly about 20 cm (8 inches) away
from the microphone.
5 To stop recording, press {OK}.
6 {OFF}
Using a prerecorded greeting
message
If you erase or do not record your own
greeting message, the unit plays a
prerecorded greeting message for
callers and ask them to leave
messages.

Hello folks, I offer no guarantee on this but it worked for me.
1. record own greetings >menu>answering device> record greeting>then after recording own greetings press OK
2. Erase own greeting just recorded >menu>answe...device>erase messa...>erase greet...>Ok
3. Then try Menu> answering device>play greeting....voila. Prerecorded message plays.
Hope This helps.

when your greeting answers, punch in your code, usually a 4 digit code, each manufacturer has their own default code that it comes with.. check the manual or website

I read thru the manual. There is nothing bout recovery of factory messages. If you recorded your own, try deleting it. Or unplug the base from power and try a reset. This is from the manual. At the end, I gave you a link to the manual!

Using a pre-recorded greeting
message
If you erase or do not record your own
greeting message, the unit plays a prerecorded
greeting message for callers
and asks them to leave messages. If the
message recording time (page 39) is set
to “Greeting only”, caller messages
are not recorded and the unit plays a
different pre-recorded greeting message
asking callers to call again.


http://service.us.panasonic.com/OPERMANPDF/KXTG9331.PDF

If you press the Greeting Check button and only the pre-recorded greeting plays back, The other greeting has been accidentally erased.

To erase a greeting, press and hold the erase button while you are listening to the greeting. The unit will announce that the greeting has been erased.

Also, it should be noted that if you're reading tajen's excellent answer and saying to yourself: "3 digit code...???"

If you've never programmed one your default code is 123.