CHANGE RINGER TONE

At an educated guess sounds like dial tone is set to decadic if there are two phones the other phone will set off ringer when numbers dialed. May need to get phone provider to change dial mode in exchange line interface circuit to be Dual tone Multi Frequency Dialing and then switch phones to Tone dialing rather than pulse dialing.

http://service.us.panasonic.com/OPERMANPDF/KXTGA101.PDF

When you get to ringer settings press select, then using the arrow keys scroll to ringer tone, choose one of the tones or melodies then select save and then select off to get out of the menu you should have chosen a new ring tone.

This phone does not allow you to change the ringer tone. You can change the volume (page 18), the voicemail tone (page 36) and the incoming call tone number (page 42). For full details see the referenced pages in the manual.

While the phone is on standby, press vol/bell to hear the current ringer tone. Press vol/bell again while the tone is ringing to switch to the other ringer tone. The last ringer tone heard will be selected as the phone's ring tone setting.



Get the manual from: http://www.google.com/url?sa=t&source=web&cd=9&ved=0CFcQFjAI&url=http%3A%2F%2Frsk.imageg.net%2Fgraphics%2Fuc%2Frsk%2FSupport%2FProductManuals%2F4300257_PM_EN.pdf&rct=j&q=presidian%20cordless%20phone%205.8ghz%20user%27s%20guide&ei=wPopTpSkE8zPmAXFhuitDA&usg=AFQjCNFGoj6kwkI8m_Hhi9K1t49wifNP2g&cad=rja

First Option:
You Go to Phone Setting in ringtone setting and check the Ring tone Setting If Ring tone Setting Ok But Not Ringe tone So
Secne Option:
Your Phone Ringer Default So Please change Ringer
And Ringing Problem will Solved Quickly

1 Press (MUTE/FUNCTION).
2 Scroll to “Ringer setting” by
pressing öor ñ, and press á.
3 Press áat “Ringer volume”.
4 Select the desired volume by
pressing öor ñ.
•Each time you press öor ñ, the
volume will change and ring.
•To turn the ringer OFF:
press örepeatedly until “Off ?” is
displayed.
5 Press á(Save key).
•A beep sounds.
To turn the ringer ON:
Press ñin step 4.
•The ringer will sound at the LOW level.
•You can exit the programming mode any time by pressing (OFF).
•If set to OFF, “Ringer off” will be displayed while the handset is not in use.
•If you have received new calls, “Ringer off” will not be displayed but
“Received calls” will be displayed while the handset is not in use.
“Ringer off” will be displayed for about 5 seconds after completing operations
or lifting the handset from the base unit or the charger.
•You can also select the ringer volume while an external call is being received.
Press öor ñwhile the handset is just ringing.
•You can change the ringer tone for external calls. See page 49.
HIGH
MEDIUM
OFF
Ringer volume
Low High
Ringer volume
Off ?
LOW
ñ
ñ
ñ
ö
ö
ö
V.M. access
HRinger setting
Initial set
--------------
HRinger volume
Ringer tone
18
LCD

Without the exact model it is difficult to find the manual.

Here the manual for 900 series/996:Uniden EZI996.

I also quote from manual:

Selecting the Ringer Tone and Volume

Base ringer on/off
The ringer switch allows you to set the base ringer on or
off. If you set the switch to off, you never hear the base
ringer tone.

Base ringer tone
Press the ringer tone button in standby mode to select one of 7 ringer tones.

Base ringer volume
Slide the ringer volume adjuster to set the base ringer volume.

Handset ringer tone and volume
Press the volume up key or volume down key (labeled as the volume/ /+ or volume/ /- key) in standby mode to select one of five ringer tones and volume combinations

Base unit ringer tone
(use either the handset or the base unit)
Make sure the base unit is not being used.
Setting the base unit ringer tone by using the
4 Select the desired ringer tone by pressing [d]
or [B].
• The handset will ring and the ringer tone will
change. If the ringer volume has been turned off,
the handset will not ring
• You can also select the ringer tone by pressing [1]
to [7].
5 Press Save, then press [OFF].
Press VOLUME [<] or [>], then select the desired ringer tone by pressing
[1] to [7].
[1] to [3] : Bell ringer patterns [4] to [7] : Melody patterns
• After pressing VOLUME [<] or [>], the base unit will ring using the current ringer
tone.
• The base unit will ring and the ringer tone will change.
• To stop ringing, press [STOP].
1 Press [MENU].
2 Scroll to “Initial setting” by pressing [d] or [B], then press
Select.
3 Scroll to “Set base unit” by pressing [d] or [B], then press Select.
4 Press Select at “Ringer tone”.
5 Select the desired ringer tone by pressing [d] or [B].
• The base unit will ring and the ringer tone will change. If the base unit ringer
volume has been turned off, the base unit will not ring
• You can also select the ringer tone by pressing [1] to [7].
6 Press Save, then press [OFF].

This Can Be Found On Page 17 And 18 Of The User Guide.

If You Do Not Have The User Guide It Can Be Downloaded Here
http://support.radioshack.com/support_phones/doc73/73355.pdf

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This is the best I can do to answer part of your problem. I solved my problem by taking this advice from Uniden for their dual phone set:
Selecting Ringer Tone (handset only)
Question:
How do I set/change my ringer tone on the handset?

Answer:
There are two different way to change you ringer tone depending on which model you have.
If you do not have an option in your menu on you handset for handset setup, then you will simply hit the volume ^ or v arrows on the handset rapidly scrolling through the 2 ringer tones and volume combinations.