I don't know of anything that will circumvent your texting limit and still show your current cell number as the sender. Long term, Google Voice is probably the best choice for transparency and interoperability; you'll have to advise people of your new number this one time, but people can call or text that number and reach you, and texts/calls from you will appear to be from that number as well.
In fact, if you're not under contract, or are willing to break your contact, you can do all this without anyone else being aware of it, by porting your current cell number to Google Voice and getting a new number for your cell phone. I did this about 18 months ago and never told any of my contacts. I've had 3 different cell phones and 3 different cell numbers since then, and it's been completely transparent to everyone.
I was recently testing the Moto X and Nexus 5 concurrently, and calls to my Google Voice number tang on both phones, texts were delivered to both phones, and calls from either phone appeared to be from my Google Voice number. Nobody knew which phone I was using when, or even that I had multiple phones.
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