A number of early adopters of Microsoft's Windows Phone 7 reporting issues when connecting to Wireless Network. This's because Microsoft isn't helping users to know their MAC address within WinP7 mobile operating system.
A number of users tend to implement MAC address filtering for security on their routers; this means that they can stop anyone accessing their network unless they've the correct MAC address.
The problem here is that Microsoft doesn't seem to allow anyone to find out what their MAC address is, so entering it into your router becomes more difficult. The only way at present is to open up your network and try to find out the phone's MAC address. This's not exactly the easiest and safest route and certainly not the way it has been in the past for nearly every other Wi-Fi based smartphone on the market today.
Posts on the Microsoft Answers forum and on the Internet have had responses from Microsoft MVP's who've also stated that this's the only way around the issue at present.