Because I work for RIM, there is a general employee directive to not give any technical support online. So this article relates to all cell phones in general. I certainly don't want to get fired. (Ssssh! They don't know about this blog). Oh yeah, almost forgot:

The postings on this site are my own and don't necessarily represent the position, opinions or strategies of RIM

You might also be interested in my general description of UMA, and whether you can get free long distance over UMA.

"how does UMA connection work"

Normally your phone sends its signals to a cell tower, which forwards it to a server on the carrier's network. With UMA, your phone logs into the carrier's network through your internet connection and sends its signals directly to that server. That means you can access all of the same services over UMA, like voice, data, and SMS. Unfortunately, it means that all of those same services go through your carrier's network, perhaps unnecessarily. Some phones support something called "Internet Offload", in which UMA is only used for voice calls, but all the data goes directly over the Internet. Got it?

"connecting a uma phone to the network."

Connecting UMA is hard. Normal cell phones are designed so that any idiot with a bank account can use them. But unfortunately, UMA is based on the Wifi network, and Wifi has a lot of lot of things that you can screw up. To connect to UMA, six things have to happen:

1. Your cell phone has to be specifically designed for UMA. It has to contain a Wifi radio on it, or it just isn't going to work. You can't take your 10 year old Motorola and sign up for UMA service. It has to be fairly new -- probably made in the last two years. Furthermore, it has to contain the UMA software on it. You pretty much have to have the phone and OS designed to accommodate UMA, because the UMA application needs direct access to secure sockets, audio, and SIM card security functions.
2. You have to sign up for UMA service with your carrier. Their security gateway knows whether you are paying for their service and it won't let you through if you didn't sign up.
3. You have to have the security certificate installed on your phone. Each carrier (for example, T-Mobile, or Rogers in Canada) has a certificate that has to be loaded onto your phone for you to connect. It is kind of like a password, but it is far too long to type in manually, so it has to be loaded with special software. This probably happened when your phone was manufactured and customized for the carrier. Unfortunately, that means that it is locked to a particular carrier, unless you can figure out a way to load a new certificate. This is what gives people problems when they try to use a phone bought on ebay.
4. You have to successfully connect to Wifi. This will involve scanning for the Wifi network using your phone, and probably entering a WEP or WPA password of some kind. You should try this on your laptop first, to see if your Internet is set up properly. If your laptop can't connect, then there is some other problem with your Wifi router.
5. Your phone has to be configured to use the UMA connection. The mobile phone standards dictate that all phones have to have some way of choosing how UMA is used. You have to be able to choose between cellular-only, cellular-preferred, UMA only, and UMA preferred modes of operation. The only option that makes sense is UMA-preferred. (This is sometimes called "Wifi preferred")
6. Finally, UMA must successfully connect. Turn off your microwave oven. Stop bittorrent. At this point, one missed packet can cause a huge delay. The connection phase retry can take up to 32 minutes, because the mobile standards describe a precise scheme of retries. Specifically, it tries three times, waiting 30 seconds between tries. If those tries fails, it waits 2 minutes, then tries three more times. On failure, it doubles the two minutes to 4 minutes, and so forth, until it eventually waits 32 minutes between retries. Then it stops doubling the timeout. To avoid the 32 minute wait, you can probably make it try again immediately by turning off and on the phone.

"how to use uma phone without sim"

It is not possible to use UMA without signing up for an UMA plan with a carrier. That is because the SIM card actually performs the authentication process to login to UMA. No SIM means no UMA.

"does uma work over different carriers"

If you travel, you can use your UMA phone to connect to your home carrier and make calls without roaming charges. Your main problem will be connecting your phone to wireless hotspots, because often you will have to login to the hotspot and click "I agree" to some usage agreement. If your phone browser isn't able to display the button, then you won't be able to connect to Wifi. But if you pass this hurdle, your phone should work fine. Just make sure it is actually using the UMA network when you make your call. In this case, it might be good to set it to UMA only mode.

"how to make uma server"

So you want to make an UMA server so you can run your own phone service. Okay, well, first you have to remember that UMA is simply a wrapper around the regular cell phone messages so they can be transported over the Internet. So all you have to do is implement the entire rest of that phone network. Feel free to download the 3GPP specifications and implement your own phone network. Don't let me stop you. Out of the 1,000,000 pages of telephony standards, I think you'd only have to read about 50,000.

Or you could just go write a SIP server like a normal person.

"which carriers have uma"

Umm, I don't know. I know T-Mobile US is doing it and Rogers Canada is as well. There is a complete list on wikipedia.

"best uma phone"

The best UMA cell phone is the BlackBerry, which does support Internet Offload. The latest model at this point is the 8900. Go out and buy that one as soon as you can. But be careful if it is used.

"UMA skype"

Skype shouldn't be used over UMA, because as I have said, on most phones, all data goes through the carriers servers, and is chargeable. Your Skype usage would cost thousands of dollars in data charges. If your phone supports Skype and Wifi, and you can turn of UMA, do so to avoid these charges.

"is uma service free"

That depends on your plan and contract. You did read it, didn't you? Usually you have to pay extra for UMA, but then you get unlimited calling while on UMA. But read your plan very carefully.

If you make long distance calls, you will probably be charged extra.

But the number one search topic for UMA is:

"uma nude"

I don't have all the answers about UMA! For that, you'll have to look elsewhere.