Just about all T-Mobile voice mail plans provide “fax mail”. Someone can send a fax to your mobile phone number and the voice mail system holds it there. When you check your voice mail you can specify the number of a fax machine to which to forward the fax. Handy when traveling and you want the fax wherever you are.

Update: Fax mail may be turned off by default(!), mine was. Call customer service to get it turned on.