Smarty is Three, same coverage, same company. Different support, different backhaul.

First the bad:

I got a Smarty Unlimited data sim. It connected at a good rate, though the routing was a bit odd, and the IP address you get is NATted, unlike the Three equivalent.

However, every 20 seconds or so, I was given a new IP address - normally the next one up the range. Connections using the old IP would just hang. Then 20 seconds or so later, the IP would switch back. But 40 seconds was too late, so the old sessions had all timed out.

I phoned support, who were totally useless. Repeating that it wasn't a fixed IP service and that they reallocate unused IPs. Refused to say whether my problem was due to a network fault.

Refused to put me through to someone who knew what they were talking about, so I cancelled and got my money back - six weeks later.

I suspect that they were working on the network, but the small saving compared to Three itself just wasn't worth it.

Now the good:

A Smarty 3GB Sim at £7 per month gives unlimited calls and texts on the Three network. Use less than 3GB of data in a month and you get £1 per GB (pro rata) back on the next month's bill.

Using wi-fi almost all the time, so hardly any mobile data use, this means that phone gets unlimited calls and texts for just £4.20 per month. Absolutely superb value!