I have 3 of them working fine, and we ran a sim thru mums one for her to register and that went fine as well.
message cannot be displayed happens on occasion on incoming texts I found when on vodafone, but thats from asian handsets writing in some other charset, or a mms coming thru to it (with no way to retrieve which sucks)
Never had outbound issues on them at all. Infact I never put a SMSC into it - just worked. And the clock will set itself too which is great.