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You will need a PBX of some sort as you cannot easily call directly between phones.<br />
If you have the normal cisco firmware on the phones you will need cisco call manager or the express version which can run on some routers.<br />
Alternativly you may be able to get the SIP firmware for the phones depending on what model you have and then you can use other PBX's or internet voip providers.
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I have the same setup as you, except that I use 3Com. I don't see any Layer1 problem with this setup.
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I intend to use CallManager Express on the Cisco routers<br />
<br />
50centos<br />
You mean use use 3com and Cisco products? 
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What phones do you have?<br />
If you are not using Cisco switches then you may have problems with older phones as they use a different Power Over Ethernet standard.<br />
Apart from that as long as the switches you use support QOS you will be fine.
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I am yet to buy the Cisco IP Phones and routers that support Callmanager Express. At the moment I have trendnet switches. I want to buy harware that will work with the trendnet switches if possible. 
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If yo are buying phones new then they will certenly be compatible with the newer POE standard.<br />
<br />
Are the trendnet switches POE?<br />
Are they also support QOS?
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sorry i how do i check if they are POE and support QOS?
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Have a look in the manual or lookup the spec on the internet if you can find the model number of them.<br />
<br />
If you post the model number I can take a look for you.
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Trendnet TE100-S24 10/100Mbps
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The switch does not support QOS or POE.<br />
<br />
Voice is very supceptible to packet loss and as little as 1% packet loss can easily be heard. One problem can occur where if a computer is transferring a large file all the bandwidth of the ethernet link can be used. If voice is also being transferred over the link then when packets have to be dropped because of insufficient bandwidth there is a change that the voice packet may be lost. QOS prioritises the packets so if one does need to be dropped it is a normal data packet and never a voice one which is dropped.<br />
Not having QOS in the switch is not a great problem though. Windows networking is not very efficient and you dont have a server connected to a gigabit port so the chance of getting a port saturated is extremely remote. The only thing you will have to be careful if is that you dont connect a small switch off the larger switch in the event that you run out of ports. If you do do this then make sure there are no phones connected to this small switch because there is suddenly a very real chance that the link will become saturated and disrupt any voice calls going over it.<br />
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POE is a bit more of a problem as the Cisco phones need to be powered over the ethernet connection. However there is a solution in that you can use a Midspan device such as the PowerDsine range (<a href="http://www.microsemi.com/PowerDsine/Products/Midspan/PD_6000.asp" rel="ugc">http://www.microsemi.com/PowerDsine/Products/Midspan/PD_6000.asp</a>) which is what I use. This sits infront of the switch and adds POE support.
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grblades<br />
confirm if i got u right. I can have my the following setup<br />
Cisco IP Phones-&gt;Midspan device-&gt;Trendnet Switch-&gt;Cisco Router with CME-----E1 Link---Cisco Router with CME-&gt;Trendnet Switch-&gt;Cisco &nbsp;IP Phones &nbsp;<br />
OR<br />
Cisco IP Phones-&gt;Cisco Switch-&gt;Trendnet Switch-&gt;Cicso Router with CME-----E1 Link---Cisco Router with CME-&gt;Trendnet Switch-&gt;Cisco Switch-&gt;Cisco &nbsp;IP Phones ? 
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<div class="content wysiwyg-content">
I once asked a similar question. If i have Cisco IP Phones does that connectivity work?<br />
Cisco IP Phone-&gt;Cisco Switch-&gt;Trendnet Switch-&gt;Cisco Router-----E1 Link-----Cisco Router-&gt;Trendnet Switch-&gt;Cisco Switch-&gt;Cisco IP Phone<br />
<br />
Or i need cisco devices only?<br />
<br />
&nbsp;
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I once asked a similar question. If i have Cisco IP Phones does that connectivity work?
Cisco IP Phone->Cisco Switch->Trendnet Switch->Cisco Router-----E1 Link-----Cisco Router->Trendnet Switch->Cisco Switch->Cisco IP Phone

Or i need cisco devices only?

 

IP Phones Connectivity

Voice over IP (VoIP) is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Other terms commonly associated with VoIP are IP telephony, Internet telephony, broadband telephony, and broadband phone service. The term specifically refers to the provisioning of communications services (voice, fax, SMS, voice-messaging) over the public Internet, rather than via the public switched telephone network (PSTN).  Examples of the VoIP protocols are H.323, Media Gateway Control Protocol (MGCP), Session Initiation Protocol (SIP), H.248 (also known as Media Gateway Control (Megaco)), Real-time Transport Protocol (RTP), Real-time Transport Control Protocol (RTCP), Secure Real-time Transport Protocol (SRTP), Session Description Protocol (SDP), and Inter-Asterisk eXchange (IAX).

Voice Over IP

A switch is a device that filters and forwards packets of data between LAN segments. Switches operate at the data link layer or the network layer of the Open Systems Interconnection (OSI) Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs. A hub is a connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports; when a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.