Setting the Telephone Other Properties

I am trying to do some bulk updating of AD accounts using set-aduser.  The fields I am having a problem with are located on the Telephones tab of ADUC. Beside each field on that tab is a button called Other.  When I run get-aduser -properties * on a user that doesn't have any of those properties set nothing appears.  However, if I manually set the Other button beside the Mobile field and run get-aduser -properties * I see othermobile appear with the data I have entered.

My question is how can I populate that field using powershell?  I have tried using the set-aduser command but I get the following error message

Set-ADUser : A parameter cannot be found that matches parameter name 'othermobile'.

Any help is appreciated.

Thanks,

Andy