So inbound, agree with Eton radio.
Outbound, either a phone with texting, or a tablet with cellular.
texting is 1/50th the bandwidth of calling, and can slip through in any lull.

A twist on this- If you have one of the kindles that has a cellular connection- you already have a basic ability to do this- there is a browser built in- Not PRETTY, but works.

Plus, WAY GOOD battery life.

Unrelated tip- look for refurb tablet at places like cowboom or newegg--
today 12-7-15 cowboom has a older model Galaxy Tab 3 Verizon 3g for 34.99 U.S.