Need a basic manual so I can learn basic steps to make my phone effective. at present cannot retrieve messages from previous callers.

Well, if it's an iPhone I may be able to help :) once you delete a voicemail from your log, it'll go to deleted messages. Scroll to the bottom of your voicemails for the deleted messages button and there you can retrieve all deleted voicemails. Now, if you deleted your voicemail from there too, then your best bet would be calling your phone company and see if they could possibly retrieve it. Again, this is for an iPhone, I'm not sure how it works on any other device. Hope that helps! :)

As a matter of fact, every time you sync data between iPhone and iTunes, all previous data will be automatically backed up by iTunes and stored as a .sqlitedb file, which will be updated along with the later sync continuously. But those backup files can't be viewed or taken out unless you use some software using special algorithms to extract.

Learn how to recover your iPhone message with step by step guides.

You can get the user manual here
http://www.samsung.com/us/support/downloads/NP-R580-JSB1US

Samsung SGH-S366 Quad Band Flip Phone User Manual:

copy and paste this link into your internet browser to see:

http://downloadcenter.samsung.com/content/UM/201005/20100527063315859/S366_UG_English_Final.pdf

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There is only a limited numbers of previous callers
in a phone, since this is automatically erase as
programmed. The answer to your question is yes,
if and when your caller is not yet erased. You can inquire your telephone company, how many callers can your phone hold, before it is erased.

For voice mails, you can check your call log and in missed calls deduce caller from the time of the message?!

Here is a link to the site containing a pdf manual link and this is an excerpt for you :

Long Distance calls and Area Code Setting/Cancellation
While the present Caller ID information is displayed, pressing */tone/< will place
or remove the prefix "1" in the display to set the call for a long distance call, or
pressing #/> will set or cancel an area code (see page 30).
Storing Caller ID messages in the Phonebook
Messages shown in the Caller ID list can be stored in the phonebook. The phone
number and name of the party on the Caller ID list can be stored in memory.
1) When the phone is in standby mode, select the Caller ID message to be stored.
Then press the STORE soft key on the base or the EDIT soft key on the handset.
From the handset, then select E D I T ?. S t o r e / E d i t N a m e appears. If the Caller ID
message is already stored in memory, you will hear a beep and T h i s d a t a i s
a l r e a d y s t o r e d ! ! appears. The number will not be stored.
2) To complete the setting, follow the steps 3-8 in "Phonebook (Storing Phone
Numbers, Names, Distinctive Rings, and Speed Dial)" on pages 42-43.

The KX-T7456 is a proprietary system phone. You have a Panasonic phone system and a voice mail, both separate items with their own part number. Your phone can work on several different systems and use different voice mail so your first step is to determine the part numbers from the system and voice mail. Then you will need a "programming" manual or possibly "administrator's manual" NOT a "user guide" for at least your voice mail and maybe for the system as well.