Validate Sri Lankan phones numbers and get their carrier

lkphones.ts

export module LKPhoneValidator
{
    export function Validate(phone : string) : PhoneValidation
    {
        // remove starting +94
        phone = phone.replace("+94", "0");

        // Consider number length
        if ((phone.startsWith('0') && phone.length == 10) || (!phone.startsWith('0') && phone.length == 9) && /^\d+$/.test(phone))
        {
            if (phone.startsWith('0'))
                phone = phone.substr(1);

            var carrier = null;
            var starter = phone.substr(0,2);

            switch (starter)
            {
                case "70" :
                case "71" : 
                    carrier = CarrierType.Mobitel;
                    break;
                case "72" :
                    carrier = CarrierType.Etisalat;
                    break ;
                case "75" :
                    carrier = CarrierType.Airtel;
                case "76" :
                case "77" :
                    carrier = CarrierType.Dialog;
                    break;
                case "78" :
                    carrier = CarrierType.Hutch;
                    break;
            }

            return new PhoneValidation(true, carrier, starter)

        } else {
            return new PhoneValidation(false, null, null);
        }
    }

    export enum CarrierType
    {
        Airtel, Dialog, Mobitel, Etisalat, Hutch
    }

    export class PhoneValidation
    {
        Valid : boolean;
        Carrier : CarrierType;
        Starter : string;

        constructor(valid : boolean, carrier : CarrierType, starter : string)
        {
            this.Valid = valid;
            this.Carrier = carrier;
            this.Starter = starter;
        }
    }
}