I would definitely follow Steve's advice.

AFAIK only Orange have this ridiculous practice of refusing to issue a
3g sim if requested - I'm about to move my main (Orange non 3g sim)
number into my Orange Business contract as an additional sharer and put
it into an Orange M3100. Will Orange supply me with a 3g sim (I don't
even mind paying!)? No.

AFAIK most other providers don't even have different sims for 3g and
non 3g any more - when I asked T-Mobile, they didn't even understand
the question, and eventually someone at T-Mobile told me all their new
sims are 3g anyway.

As an Orange customer for nearly 10 years, my data usage is now 100%
T-Mobile; not only do I have 3g but HSDPA. On the Business Tariff I
took out recently with Orange, I should have had 2 months free 'Try 3g'
- this was removed from my account in error after just over 2 weeks,
but because this particular offer no longer existed by then, they were
unable to correct their error!

Regards

Simon Clark
Business Telecoms