well lets give this a try.

run the following in SSMS when you are logged in to your remote mobile client

SELECT session_id,login_name,host_name

FROM sys.dm_exec_sessions

where session_id > 50

it will list all users currently logged into your SQL Server instance and the host they are connected from. Not sure but it will probably be null for your remote client. you can use this to identify what user is being used when you login.

A guest account should exist in all databases but it should be disabled by default. Since you are unable to see the guest account i have to ask what are your permissions on the server and database?

as for SA, i wasn't suggesting to disable the account just not to use it in the context that you were.