A number of customers use email to sms gateways to receive alerts. Unfortunately many of these use the sender address to either route or charge their customers account. If more than one of our customers has an account with them this can lead to sms messages being lost and/or the wrong account being charged.
The easy answer would be for the gateways to charge/route based on the receipient address rather than the sender or to allow a unique identifier in the subject or body of the message as some gateways do rather than working on the assumption that no 2 customers will ever have messages sent from the same address.
We have just updated our systems to deal with the issue regardless of who your gateway is.
Email to SMS contacts now have an extra option 'unique sender address'. Enable this and you will be given a unique address to add to your gateway as a valid sender and all messages sent to that contact will be sent from the unique address instead of our standard one.
Your messages will then be charged and routed via the correct account at the gateway.