Befor you start replacing the icons - make a copy of main.py in /usr/share/pyshared!!! You need Root rights to do this.
Unpack wammu.tar.gz and then:
1) become root rights (maybe gksu nautilus)
2) search usr/share/wammu folder
3) make a copy of the icon folder (maybe icon-old)
4) replace the icon folder with the new one
5) search for usr/share/pyshared/wammu folder
6) search for main.py (make a copy if not done before!!!)
7) replace the main.py with the new one
You can also change the icon Size by hand:
Line 165 - replace 16 with 32
Line 168 - replace 16 with 32
Line 195 - replace 16 with 32
Make a copy before you do something like this!
You can also change the icon with other one like iPhone picture ore paint yourself.