Since offering Pages, Google+ has issued a long string of numbers for the URL. This practice was certainly acceptable for linking to your profile from your website and email footer, but it caused limitations when promoting your Google+ Page offline.
While you could place your Twitter profile on your business card or your Facebook URL in a print advertisement, it would not be effective to share a profile URL such as “https://plus.google.com/118003559483403504374/,” requiring someone to type out the string to reach your Page.
You may be familiar with the custom URLs offered by Facebook. Google+ custom URLs come with slightly different rules.
Number of Fans and Followers — Facebook allows you to choose a custom URL after attracting 25 fans. Google+ only requires 10 followers to qualify for a custom URL.
Time — A Facebook Page could go live today, attract 30 fans in one hour, and qualify for a custom URL. Google+ requires a page to be at least 30 days old.
Customization — Facebook Page URLs are truly customized. A business can use their law firm name or a keyword: SEO | Law Firm – Legal Marketing chose “lawyerwebsites” (https://www.facebook.com/lawyerwebsites) as their URL. Google+ chooses your “custom” URL, which is generally based on your domain name. In some cases, the site may recommend more than one URL—based on your business name or domain name—but you have to choose from the options Google+ gives you. No creativity allowed.
One similarity both networks share is the prohibition of sale. As neither network wishes to create a new market of URLs, you may not sell or transfer either a Facebook URL or a Google+ URL.
Overall, this enhancement will help Google+ become more popular and make it easier for you to attract followers to your law firm's page. After a custom URL is selected, links to your old number-based address will redirect, so you don't have to worry about losing traffic.
As soon as you receive the notice to update your URL, take advantage of this new feature.
Before and After
Before claiming URL: https://plus.google.com/118003559483403504374/