Cisco IP phones

Can you assign 2 extensions to 1 phone? If so, how?

Yes, not sure. I have two lines on my phone, one is a routed extension from phone tree other is a DID.

Should be able to assign them in call manager just fine as long as it is a 2+ line phone. I did it many times with 7942g model phones.

Phone depand but usually you can assign as many lines as there are line keys on the phone.

SIP? CCM? what phone? need more info but generally the answer would be yes

Depends on model of phone and how depends on what firmware version your running..
But generally you can add multiple extensions.

If your using CUCM/CME, Cisco has some great guides (eg http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucme/admin/configuration/guide/cmeadm.html)

If your using SIP and rolling your own XML files then in the MAC.conf.xml file just add the extra extensions.

<line button="2">
<featureID>21</featureID>
<featureLabel>Line 2</featureLabel>
<speedDialNumber>1002</speedDialNumber>
</line>

also a cool thing is setting the FeatureIDs:
1 last number redial
2 speedial
3 hold
4 transfer
5 fwd all
9 Normal Line
19 Private
21 SpeedDial
22 Paging

A great resource is: http://www.voip-info.org/wiki/view/Asterisk+phone+cisco+7970+SIP

If you having Issues, PM me.

It depends on what phone's you have really. CME and CUCM can both have multiple extensions on most phones.