choosing a SIM card
Not all SIM cards work equally in the TC35 and my results (August 2014) are as follows:
O2 and those networks using O2 such as GifGaf and Tesco do not work, in fact the O2 card shut the TC35 down as soon as I tried to access it.
Vodaphone Looked like it might work but could not be activated until credit is added. As I was unwilling to add £10 just to try it out I abandoned this network.
EE, which includes Orange, One 2 One and T Mobile This SIM card arrived ready activated and worked with no problems. The SIM did not need activating and worked in receive mode without adding any credit. It came with a Top Up card and once I had added £5 I was able to send SMS messages from the TC35 in response to messages sent from my phone.
Asda Mobile This is my favourite. Asda now use the EE network and their card comes with a small amount of credit. The card is activated by sending a text message or making a phone call. You have to request a Top Up card and this takes about a week to arrive. In August 2014 the rates were much better than EE! £5 credit gives 2000 text messages over a 30 day period. At the end of this period text messages cost 4p compared to 12p from EE!
None of the network providers web sites was easy to follow if all you wanted was a pay as you go SIM and did not want to attach a debit or credit card to the phone number.