Yes, CALLS is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, L 1, L 1, S 1.

Is it a valid word?

CALLS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a telephone connection
a special disposition (as if from a divine source) to pursue a particular course
a loud utterance; often in protest or opposition
a demand especially in the phrase "the call of duty"
the characteristic sound produced by a bird
a brief social visit
a demand by a broker that a customer deposit enough to bring his margin up to the minimum requirement
a demand for a show of hands in a card game
a request
an instruction that interrupts the program being executed
a visit in an official or professional capacity
(sports) the decision made by an umpire or referee
the option to buy a given stock (or stock index or commodity future) at a given price before a given date

assign a specified (usually proper) proper name to
ascribe a quality to or give a name of a common noun that reflects a quality
get or try to get into communication (with someone) by telephone
utter a sudden loud cry
order, request, or command to come
pay a brief visit
call a meeting; invite or command to meet
read aloud to check for omissions or absentees
send a message or attempt to reach someone by radio, phone, etc.; make a signal to in order to transmit a message
utter a characteristic note or cry
stop or postpone because of adverse conditions, such as bad weather
greet, as with a prescribed form, title, or name
make a stop in a harbour
demand payment of (a loan)
make a demand, as for a card or a suit or a show of hands
give the calls (to the dancers) for a square dance
indicate a decision in regard to
make a prediction about; tell in advance
require the presentation of for redemption before maturation
challenge (somebody) to make good on a statement; charge with or censure for an offense
declare in the capacity of an umpire or referee
lure by imitating the characteristic call of an animal
order or request or give a command for
order, summon, or request for a specific duty or activity, work, role
utter in a loud voice or announce
challenge the sincerity or truthfulness of
consider or regard as being
rouse somebody from sleep with a call

Also: phone call, telephone call, margin call, call option, call up, shout out, send for, call in, call off.