3COM 3100 entry phone, how to configure SIP

Is your phone connecting to a hosted PBX provider or is it connecting to a premise-based IP PBX? Incoming and outgoing calls are usually handled by two separate connections between your PBX and the service provider SIP trunk. Sounds like a registration problem with the SIP trunk. There is nothing you can do from the phone itself to fix this.

go to this website and go to customer support www.polycom.com

Ok first try these step process if you have:
Roku 2 (Model 2720) - http://support.roku.com/entries/27936640-Roku-2-Model-2720-Setup-Instructions
Roku 2 XS(Model 3100) - http://support.roku.com/entries/27940370-Roku-2-XS-Model-3100-Setup-Instructions
Try to reboot again if still have problem and after all Roku will not connect than try to reset your router or configure your router with your ISP. For router configuration and set-up Linksys Support .

For 3Com that would mean a 3100 series or 3500 series phones. The 3100 series phones are for NBX and VCX phone systems and the 3500 series phones are for VCX only. Both are also SIP compliant.

You can't. The 1100 and 2100 series 3Com phones aren't SIP phones. Only the 3100 series phones can be used.

I guess you're new to this. The phone may have music on hold, it depends on the model but is generally something you have when using a pbx.
No phone has a sip trunk, that is what you connect to with your voip provider. You need to setup a sip account with a voip supplier and program your phone with the settings provided by them.

The phone is intended to be connected to a Mitel PBX telephone system. If you're using the phone at home, you must set the phone in Teleworker mode and use the IP address of the teleworker server. This will allow your phone to tunnel into the phone system.

OR the phone must be set up in SIP mode. Press and hold the 6 key while booting the phone. You will also need to set it up and tell it where the SIP server is located (IP addresses).

If you don't have this information, you should contact your vendor or system admin for further assistance.

If you are trying to use the phone without the above servers, I have bad news - it won't work.

Here are the instructions for configuring these units for 3cx

http://www.3cx.com/sip-phones/cisco-7940.html

http://www.3cx.com/sip-phones/polycom-soundpoint.html

Since the 3cx softphone worked well, I don't see why you couldn't configure each as for 3cx and make them work as well.

The 2100 series and older aren't SIP compatible. The 3100 series are.

Yes, configure second Cisco E1 port to simulate you telcom (network side) and connect it to PB, and first Cisco E1 to your telecom provider.

On Cisco router configure voice ports, and number manupilation, so you can catch any call and redirect it anywhere (Voip, Telco, PBX).

I tryed that with Ericcson, and it didn't work until connections where like these
telco <-> Cisco VoIP gateway (E1x2) <-> PBX

PBX's are not very flexible, Cisco is.