3 are utter shite!
They block port 25 for SMTP for everything other than their own SMTP server. If you use an ISP that only uses port 25, like Pipex or Tiscali you have no other option but to use 3's SMTP server which seems to have numerous problems.
Their Indian customer support are fecking useless.
I work in the City and network coverage seems to disappear every day between 12noon and 2pm. I have to revert to using my T-Mobile broadband on my phone to check mail. The rest of the time network reception is patchy.
I would avoid!