Meaning
To be at someone's beck and call is to be entirely subservient to them; to be responsive to their slightest request.
Origin
'Call' is used here with its usual meaning. 'Beck' is more interesting. The word, although current in English since the 14th century, isn't one that is found outside the phrase 'beck and call' these days. It is merely a shortened form of 'beckon', which we do still know well and understand to mean 'to signal silently, by a nod or motion of the hand or finger, indicating a request or command'.
If the term 'beck and call' had originated prior to the 14th century we we would presumably now say 'beckon and call'. It didn't though and the first recorded use of 'beck and call' in print is in Aemilia Lanyer's set of poems
Salve Deus Rex Judaeorum, 1611:
The Muses doe attend vpon your Throne,
With all the Artists at your becke and call;
That is straightforward enough. What brings the phrase to the attention of etymologists is the confusion that some people have between it and 'beckon call'. This supposed phrase is a simple mishearing of 'beck and call'. The mistake comes about because no one uses 'beck' any longer, whereas 'beckon' is commonplace.
'Beckon call' could be said not to be a phrase in English at all, but it is gaining some ground nevertheless. At present (January 2007) Google finds 28,000 hits for 'beckon call' and 474,000 for 'beck and call'.
The misspelling began in the USA in the early 20th century. For example, this early citation from
The Modesto News-Herald, May 1929:
A crowd of several hundred people heard a stirring address by B. W. Gearhart, Fresno attorney and American Legion official. "Down through the history of American wars, from the Revolutionary to the recent World conflict." the speaker declared, "America always has had at its beckon call men who would give their all for their country that people might enjoy peace and freedom.
The rogue phrase still appears in print in newspapers. Here's a recent example from the London
Daily Mirror, by Phil Differ and Jonathan Watson:
"He [football manager Dick Advocaat] told me what he was particularly looking forward to when he comes to Scotland and that's having the entire Scottish press at his beckon call and I promised he won't be disappointed."
Just because 'beckon call' is based on a mishearing that doesn't mean it won't one day become accepted as proper English. Other phrases, like '
beg the question' for instance are routinely used incorrectly by so many people that the incorrect usage has now become the standard. Let's hope 'beckon call' dies a natural death, not only because it is essentially just a spelling mistake but because its adoption would signal the last gasp of the enjoyable little word 'beck'.