What is a "Solo"?- US Attorney Carolyn Elefant is America's Number One Solo
I suppose we should let Attorney Elefant explain it in her own words;

"The way I like to tell it...I'm the head honcho in my own law firm (that one is on Facebook)...a big law firm wasn't big enough. Not big enough for my ego...I was a lawyer ahead of schedule...the first generation of lawyer-bloggers...the first to recognize and harness the power of the Internet...the first generation of law firms on-line... the upload of a law firm website (which I handcoded myself) in 1995...business owner long before the dotcom boom of the late '90s...solos know strategies associates need to learn...as an associate, you don’t own your law firm...standing firm before an insulting, nasty judge...I’ve developed lasting friendships with several accomplished female solo lawyers who inspire me...Like Jack who jumped over the candlestick, we solos are nimble and quick..."

'Solo by Choice' -or- 'Solo by Necessity'
Principal Attorney with the Law Offices of Carolyn Elefant (LOCE)

Carolyn Elefant's gives the impression that her "Solo by Choice" was a decision she had made by her own volition. Not so, around 2002 Duncan & Allen, a D.C.-based energy law boutique, told her that she wasn't "partnership material" and gave her six months to find a new job. It appears she whinged "I know that I am a good lawyer. I was good enough for you to hire two years ago, and I'm just as good now. No matter what you think, I am a good lawyer and ... I will succeed at whatever I do". When six months passed and she still hadn't found any US law firm to employ her, Elefant decided to hang out her own shingle.

Well clearly it was not 'Solo by Choice' but 'Solo by Necessity' if she wanted to be a Lawyer, as no 'Big Law' firms in the US thought she was good enough to hold down a position as a Lawyer in their establishments, she had to go it alone, I suppose that is the route most of these US Solo's have had to take when 'Big Law' kicks their arse out the door.

---'Carolyn Elefant Wants to Be the Voice of Solo Lawyers'
Welcome to the pieced-together world of the solo practitioner. There's no name on the door to Carolyn Elefant's K Street office in Washington, D.C. In the waiting room, a chubby man slouches on a black leather armchair, dozing. Elefant appears, smiling and gracious. She takes us on a slightly confusing circular journey through the halls before she finds the conference room where she left her coffee cup, fag and briefcase.'
Debra Bruno Legal Times March 27, 2008 http://www.law.com
Sounds like the seedy Hank Janson 'Private Eye' story books of long ago and you certainly get that impression from her attitude of "... I had made a mistake so I was loathe to apologize" which is in keeping with Hank Janson PI ideology! Even her description of a 'Solo' above sounds like them seedy PI's blowing their own Trumpet and all that comes out is a terrible noise.

PS I always assumed Hank Janson was a tough ex cop turned writer living in the Bronx. Now I find he was a rather mild Englishman but still a great writer who's books sold in their millions. (The first sentence sounds like Attorney Elefant and the second is a bit like me ('mild Englishman')).