Why text in phone number field of Contacts turns into numbers?

I have lots of phone nos for contacts, so in switching from Ecco to Outlook I
have kept the practice of putting a name or location in the ph no. field to
help identify them, e.g. if there's a couple both with mobile nos., I put
"503-555-12121 Joe mobile" in the Other phone no. field.

My Blackberry 8830 turns the letters into numbers, making the ph no
undialable (rejected by carrier). Putting quotes around the letters doesn't
help.

I gather I can't change the label name for just one contact - so how can I
leave text yet not have it turned into a number that is dialed by my
blackberry?

SM