The My Phone Team posted the following:
The My Phone service will be down for planned maintenance from 7 AM to 10 AM PDT on 4th March (check your local time for 7 AM PDT here). Going forward such maintenance notifications will be posted as tweets on our twitter account to ensure that you can plan ahead for downtime.
We also pushed out an over the air update for the My Phone application installed on your phone to address some known issues. You will receive a prompt to download and install the update, the next time the phone syncs with your online account. We recommend that you install the update immediately as it is a fairly quick and seamless process. The update must be installed within 7 days of receiving the prompt otherwise My Phone service will stop working on your device. If due to any reason you are unable to install the update within 7 days you may do so later by navigating to http://myphone.microsoft.com/install from Internet Explorer on your phone.