I think you need to use methods, however you can use 'note' to describe the methods.
Joined: May 09, 2006
After looking up the UML 2.0 spec I tend to agree with you. The spec states:
A Message is a NamedElement that defines one specific kind of communication in an Interaction. A communication can be, for example, raising a signal, invoking an Operation, creating or destroying an Instance. [...] A Message reflects either an Operation call and start of execution - or a sending and reception of a Signal.
[Unified Modeling Language: Superstructure, version 2.0, formal/05-07-04]
Furthermore the notation of signals and operation calls are specified in great detail. IMO there is no room for a plain english approach.
subject: Sequence diagrams: methods calls vs. plain english