The East and West branch libraries now offer fax services.
(The Central Library does not yet.)

In addition, here are some other locations in Somerville that provide fax services also:

Master Printing & Signs  
60 Union Square,
Somerville, MA 02143
Phone: (617) 625-5422
Hours: 
Monday    9AM–6PM
Tuesday    9AM–6PM
Wednesday    9AM–6PM
Thursday    9AM–6PM
Friday    9AM–6PM
Saturday    Closed
Sunday    Closed

The UPS Store  
519 Somerville Ave, 
Somerville, MA 02143
Phone: (617) 591-0199
Hours: 
Monday    8:30AM–7PM
Tuesday    8:30AM–7PM
Wednesday    8:30AM–7PM
Thursday    8:30AM–7PM
Friday    8:30AM–7PM
Saturday    9AM–5PM
Sunday    Closed

The UPS Store  
411A Highland Ave,
Somerville, MA 02144
Phone: (617) 776-4949
Hours: 
Monday    8:30AM–7PM
Tuesday    8:30AM–7PM
Wednesday  8:30AM–7PM
Thursday    8:30AM–7PM
Friday    8:30AM–7PM
Saturday    9AM–5PM
Sunday    Closed

Staples
165 Middlesex Ave.  (Assembly Square)
Somerville, MA 02145
(617) 616-1113
Hours:
Monday    8:00 AM - 9:00 PM
Tuesday    8:00 AM - 9:00 PM
Wednesday    8:00 AM - 9:00 PM
Thursday    8:00 AM - 9:00 PM
Friday    8:00 AM - 9:00 PM
Saturday    9:00 AM - 9:00 PM
Sunday    10:00 AM - 6:00 PM

Marfione Studio
179 Washington St   (Union Square)
Somerville MA, 02143
Tel: 617-623-6562
Hours:
Monday  10:00 AM - 7:00 PM
Tuesday  10:00 AM - 6:00 PM
Wednesday 10:00 AM - 6:00 PM
Thursday 10:00 AM - 6:00 PM
Friday 10:00 AM - 5:00 PM
Saturday 10:00 AM - 4:00 PM
Sunday  Closed