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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-03-28</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001169264</issuerCik>
        <issuerName>SYNIVERSE HOLDINGS INC</issuerName>
        <issuerTradingSymbol>SVR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001104997</rptOwnerCik>
            <rptOwnerName>GTCR FUND VII LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GTCR GOLDER RAUNER, L.L.C.</rptOwnerStreet1>
            <rptOwnerStreet2>6100 SEARS TOWER</rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60606</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001262949</rptOwnerCik>
            <rptOwnerName>GTCR PARTNERS VII L P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GOLDER RAUNER, L.L.C.</rptOwnerStreet1>
            <rptOwnerStreet2>6100 SEARS TOWER</rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60606</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001105021</rptOwnerCik>
            <rptOwnerName>GTCR GOLDER RAUNER LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>6100 SEARS TOWER</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60606</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2005-03-28</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5806813</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>16</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>25608766</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Class A Cumulative Redeemable Preferred Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-03-28</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>65757</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1413.05</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5806813</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each share of Class A Cumulative Redeemable Preferred Stock converted into the number of shares of Common Stock obtained by dividing (1) the sum of (a) $1,000 and (b) any accrued and unpaid dividends through February 9, 2005 by (2) the per share initial public offering price of the Common Stock, which is $16.00.</footnote>
        <footnote id="F2">Pursuant to the Issuer's Second Amended and Restated Certificate of Incorporation, each share of Class A Cumulative Redeemable Preferred Stock that was not redeemed with the proceeds from the Issuer's initial public offering of Common Stock was converted into Common Stock on March 28, 2005.</footnote>
        <footnote id="F3">GTCR Fund VII, L.P. (&quot;Fund VII&quot;) is the direct beneficial owner of the shares reported in Table II. GTCR Partners VII, L.P. (&quot;GTCR Partners VII&quot;) is the general partner of Fund VII and GTCR Golder Rauner, L.L.C. (&quot;GTCR&quot;) is the general partner of GTCR Partners VII. As such, GTCR Partners VII and GTCR may be deemed to be beneficial owners of the shares reported in Table II. GTCR Partners VII and GTCR expressly disclaim beneficial ownership of the shares reported in Table II. The filing of this form shall not be deemed an admission that GTCR Partners VII or GTCR is, for Section 16 purposes or otherwise, the beneficial owner of such shares.</footnote>
        <footnote id="F4">Immed.</footnote>
        <footnote id="F5">Not Applicable</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Jody S. Gale under a Power of Attorney filed on 2/9/05</signatureName>
        <signatureDate>2005-03-28</signatureDate>
    </ownerSignature>
</ownershipDocument>
