[Nexus 7 General] GoneNomad:
Yeah, it does really suck. When I noticed that plan, I had the same thought you did: it was perfect for what I needed, and cheaper than T-Mobile's data-only MBB plans. I had already talked to a number of different T-Mobile reps, and never got a definitive answer until I stumbled upon this thread (and this one: Voice calls on 3g Nexus 7.)

But it appears that a definitive answer is here: iPad work with $30 Prepaid Unlimited Data Plan?

"This is a great question. This specific plan is targeted for smartphone users and does not have the proper settings in our billing system that will allow tablet users to be able to benefit from this plan. You would need to look at setting up a Mobile Broadband plan if you would like to be able to use your iPad with our service. Hope this helps.

tmo_adam_c"

Since it is perfect for what I needed and cheaper than T-Mobile's data-only MBB plans, naturally T-Mobile has arbitrarily decided to restrict it to "phones" only.

So, it's totally OK on a 5.5" Galaxy Note, but if you want to use a 7" device (which is easier to see, especially for older people like me) TOO BAD!

But as you mentioned above, I'm sure T-Mobile has made this decision based of the idea that the the average data usage will be greater with a tablet than a phone.

There's another big difference too: hardware price. Bigger tablets cost more, but smaller (unlocked, no contract) phones cost a LOT more. So the combination of the relatively cheap Nexus 7 and T-Mobile's $30 100/Unltd/Unltd no-contract plan would be perfect for you, for me, and a lot of other people.

-----

I registered for this site just to thank those who have been wading through this issue (especially user "phonic" for his persistence in trying to get across the difference in making voice calls via any VOIP method using the data connection, and making voice calls directly via GSM).

Since I've spent the better part of this morning wading through 50 pages of posts in these two threads (among others), in order to help the next people who come here with the same questions I had, I'd like to recap here to save them some time, which after all these pages really boils down to just these simple facts:

With no modifications, the Google Nexus 7 HSPA+ data can (apparently) receive (but not send) SMS messages, but cannot make or receive GSM voice calls. Software can be added fairly easily to allow the Nexus 7 HSPA+ to send SMS messages. There appears to be no practical way for a Nexus 7 HSPA+ to make or receive GSM voice calls.

T-Mobile offers a terrific no-contract plan here that includes 100 minutes talk, unlimited text, unlimited data (slower speeds after 5GB) for only $30 per month. This is less expensive than T-Mobile's Mobile Broadband refill cards here, which are $35 for a 3.5GB month pass or $50 for a 5GB month pass (with NO additional slower-speed data after those limits).

WalMart does offer similar $35 3.5GB Mobile Broadband pass that is valid for 60 days, but it requires that the hardware be purchased at WalMart, which usually means a higher price for that hardware than the best online deal, and fewer choices (e.g.: no Nexus 7 HSPA+ from Walmart). This Walmart $35/60 days deal is permanently locked to the IMEI number of the hardware, and cannot be transferred with the SIM card to another device bought elsewhere.

I believe the above statements are a correct assessment of the situation as of today.

If anyone else has any verified information to the contrary, I hope they will post it.