<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-04-14</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001086740</issuerCik>
        <issuerName>DELTATHREE INC</issuerName>
        <issuerTradingSymbol>DDDC.PK</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001458594</rptOwnerCik>
            <rptOwnerName>Stevanovski David</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>349-L COPPERFIELD BOULEVARD, #407</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CONCORD</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>28025</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>12% Convertible Note due March 4, 2014</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.08</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2011-04-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionTotalValue>
                    <value>250000</value>
                    <footnoteId id="F1"/>
                </transactionTotalValue>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2011-04-14</value>
            </exerciseDate>
            <expirationDate>
                <value>2014-03-04</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, $0.001 par value</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3125000</value>
                    <footnoteId id="F1"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <valueOwnedFollowingTransaction>
                    <value>800000</value>
                    <footnoteId id="F2"/>
                </valueOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By D4 Holdings, LLC</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Consists of a $250,000 advance under a Convertible Note pursuant to which D4 Holdings, LLC (&quot;D4 Holdings&quot;) has the right to convert all or any portion of the outstanding principal amount under the Convertible Note at a conversion price of $0.08 per share.</footnote>
        <footnote id="F2">The Convertible Note was issued pursuant to a Loan Agreement dated March 2, 2011 under which D4 Holdings agreed to loan up to $1,600,000 in aggregate principal amount. As of April 14, 2011, the Issuer had received total advances of $800,000 in outstanding principal under the Loan Agreement.</footnote>
        <footnote id="F3">The reported securities are held directly by D4 Holdings, LLC. The reporting person is a member of Manna Holdings, LLC, which is the sole member of D4 Holdings. As such, the reporting person may be deemed to beneficially own the securities reported herein and owned directly by D4 Holdings. The reporting person disclaims beneficial ownership of such securities, and this report shall not be deemed an admission that such reporting person is the beneficial owner of the securities for the purpose of Section 16 or for any other purpose, except to the extent of such reporting person's pecuniary interest therein.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ David Stevanovski, by Colleen Jones, attorney-in-fact</signatureName>
        <signatureDate>2011-04-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
