[buro9]

Of the UK services I've seen, none charge for incoming SMS.

The 2nd on my Google search is http://www.textover.com/incomingsms.html which states:

  We do not charge per message received.

#1 and #3 on the Google search were both a bit vague, mentioning only a fixed rate monthly charge of £5 and £7.50 per month for a number to receive messages on.

They didn't mention whether they charge per message received, but every other price is unambiguous so I'd probably read it as them not charging for receipt of messages beyond the line rental but for the sake of argument didn't want to jump to that conclusion.

The Twilio price is good though, I was finding outbound rates closer to 4p per SMS and only dropping down to 2p per SMS with serious quantity paid in advance.