fix: normalize attribute keys to symbols

lib/telephone/service.rb

@@ -20,6 +20,8 @@ class Service
     # Primary responsibility of initialize is to instantiate the
     # attributes of the service object with the expected values.
     def initialize(attributes = {})
+      attributes = attributes.transform_keys(&:to_sym)
+
       attributes.each do |key, value|
         send("#{key}=", value)
       end

spec/telephone_spec.rb

@@ -152,6 +152,19 @@ def call
       expect(subject.new(foo: "baz").foo).to be "baz"
     end
 
+    it "accepts string keys" do
+      expect(subject.new("foo" => "baz").foo).to eq "baz"
+    end
+
+    it "handles string keys with callable defaults" do
+      service = Class.new(Telephone::Service) do
+        argument :name, default: "Default"
+        argument :message, default: -> { "Hello, #{name}!" }
+      end
+
+      expect(service.new("name" => "Custom").message).to eq "Hello, Custom!"
+    end
+
     context "if there is a required argument" do
       before { subject.public_send(:argument, :required_field, required: true) }