On the issue of inbound SMS; texts to geographic phone numbers are generally, by default, presented as text-to-speech.
And,
giving your contacts a VoIP 01223 number to dial that is
forwarded to the 07 SIM will, I would suggest, enhance the project.
I use my Raspberry Pi Asterisk server to do the forwarding, but you could use a free service "in the cloud":
http://pbxes.com
You can get your SIP trunk with a Cambridge number from:
https://www.sipgatebasic.co.uk/
You could apply credit to the Sipgate account and use it to make the second leg of the call to the mobile, but there are much cheaper alternatives we can discuss.
I'd be more than happy to help configuring this with you.