MWI (Message Waiting Indicator) for VoiceMails

I have setup a voicemail system on my asterisk installation . It is working fine . Also, MWI (Message Waiting Indication) works and i have tested it on some Nokia handsets supporting this feature.
The way things are now is that whenever a user gets a new voicemail, he gets an sms like notification on his phone informing about the new voice mail , and also an email is sent to the user.
However, the MWI sender for the sms is shown as asterisk@host, where host is my server running asterisk.
Now, i have the following two questions :

  1. Is it possible to customize the MWI i.e. the message that appears in the sms like notification received by the user ?
  2. Is it possible to customize the senders number that appears on the users handset. ?

Any help/tips for implementing the above would be really appreciated.

Thank You.