You have a server that has Exchange Server 2013 installed.
You plan to configure Unified Messaging (UM) to connect to an IP-PBX.
A Telecommunications Administrator configures the following numbers on the IP-PBX:
– First extension number: 12100
– Last extension number: 12499
– Help extension number: 12500
– Incoming pilot number: 12000
You need to configure UMto support the following requirements:
Users must be able to use Outlook Voice Access.
Users must be able to receive voice mail when callers connect to the users’ extension.
Callers must be able to dial into an automated helpsystem hosted by your company,
which uses standard menus and Speech-Enabled menus.
Which numbers should you use for the UMconfigurations?
Answer: 
Explanation:
Box 1:12000
Box 2:12500
Box 3:12000
Note:
An Outlook Voice Access number lets a user who is enabled for Unified Messaging (UM) and voice mail access
their mailbox using Outlook Voice Access. When you configure an Outlook Voice Access or subscriber access
number on a dial plan, UM-enabled users can call into the number, sign in to their mailbox, and access their
email, voice mail, calendar, and personal contact information.
By default, when you create a UM dial plan, an Outlook Voice Access number isn’t configured. To configure an
Outlook Voice Access number, you first need to create the dial plan, and then configure an Outlook Voice
Access number under the dial plan’s Outlook Voice Access option.
Although an Outlook Voice Access number isn’t required, you need to configure at least one Outlook Voice
Access number to enable a UM-enabled user to use Outlook Voice Access to access to their Exchange 2013
mailbox. You can configure multiple Outlook Voice Access numbers for a single dial plan.
After you create a Unified Messaging (UM) auto attendant, incoming calls to an external telephone number that
a human operator would ordinarily answer are answered by the auto attendant. Unlike with other Unified
Messaging components, such as UM dial plans and UM IP gateways, you aren’t required to create UM auto
attendants. However, auto attendants help internal and external callers locate users or departments that exist in
an organization and transfer calls to them.
Hunt group is a term used to describe a group of Private Branch eXchange (PBX) or IP PBX extension
numbers that are shared by users. Hunt groups are used to efficiently distribute calls into or out of a specific
business unit. Creating and defining a hunt group minimizes the chance that a caller who places an incoming
call will receive a busy signal when the call is received.
In a telephony network, a PBX or an IP PBX can be configured to have a single hunt group or multiple hunt
groups. Each hunt group created on a PBX or IP PBX must have an associated pilot number. Using a pilot
number helps to eliminate busy signals and to routeincoming calls to the extension numbers that are available.
The PBX or IP PBX uses the pilot number to locate the hunt group and in turn to locate the telephone extension
number on which the incoming call was received and the extensions that are assigned to the hunt group.
Without a defined pilot number, the PBX or IP PBX can’t locate where the incoming call was received.
Reference: Create a UM Auto Attendant