I found some stuff on the internet, where somebody wanted to complete a variable-field PDF on an Iphone, and email it. IIRC, no solution was thought possible.
However it is not too hard to knock up a website form which is a GAR, which you complete online, and which has a SEND button that emails+faxes it to all 3 services (using email, and email2fax). Obviously you would to keep such a facility private
There is probably another way... short of a remote desktop solution which would obviously work but is a bizzare way to do this.
The GAR exists in both PDF and Word (.doc) forms.