Those of you with a Samsung Nexus S or Galaxy Nexus using an AT&T SIM card are now able to download Google Wallet straight from the Android Market. T-Mobile customers - as well as Verizon - will have to use an alternative method for downloading the application. It's not too sneaky, and has been confirmed by multiple users as a working perfectly.
Why Google Wallet can't be open throughout all carriers is beyond me. Those of you on other T-Mobile or 'Big Red' head to http://market.android.com and conduct a search for 'Google Wallet' on your device. During this, your phone will then prompt if you would like to open the page within the Market application, but just say no and continue within your browser. Next, select 'Install'. When it asks if you would like to open it in the Market, select YES this time. You can then install the app just like any other!
Since the Android Market application recognizes Google Wallet as a legit download, you will be able to receive normal updates. On a side note, those of you that already installed a modified version of the .APK file should definitely remove it before going through with this method. It could possibly mess up the download.