[Nexus 5 Q&A, Help & Troubleshooting] hoktrillian:
Using PC or phone to try to activate a new SIM for data only plan simply would not work. I got stuck with ConnectMe from T-Mobile web page and could not go any further. :(

As a result, I went to Walmart to buy a T-Mobile 4G Mobile HotSpot - Orange. I had visited a total of four Walmart stores. Only the fourth store still have the device in stock. The price is $49.88 plus 9% sales tax. Total came out as $54.37. The device package came with a SIM that includes 5 GB of data available for three months from first use. This means that my monthly mobile phone cost has further gone down to $18.13 from $30 as I have been using $30 per month pre-paid plan with 100 minutes talk, unlimited text and data with first 5 GB up to LTE speeds. However, my actual usage has been less than 10 minutes talk (due to wrong number or telemarketing as I do not give out this mobile phone number at all), few test texts with about a dozen free T-Mobile text messages (information from T-Mobile) and only about 600 MB data consumed each month. This is because I usually have Wi-Fi access except driving. When I drive, I can hardly use phone except making and receiving calls and check traffic condition. Therefore, I felt the $30 mobile phone service was over bought.

T-Mobile 4G Mobile HotSpot - Orange only support up to HSPA+ speeds. Once my phone was connected to the device via Mi-Fi, I opened the web browser to go to http://www.t-mobile.com/ConnectMe, it stated they had been waiting for me! I simply gave name, e-mail address, password and ZIPcode, then I was connected. Speed tests showed much slower than LTE speeds, like about 5 mbps down and 1 mbps up with over 100 ms ping. VoIP worked stationary, have not tested when driving.

Since the SIM for T-Mobile 4G Mobile HotSpot - Orange uses regular size (big) SIM, I had to cut it down to the size of micro SIM (medium) to fit into Google Lexus 5 by LG. Once the cut down size SIM inserted into Google Lexus 5 by LG and turned on the phone, it showed it is connected to LTE signals. Speed tests show about 25 mbps down and 20 mbps up with 40 ms ping. VoIP as well as all other data required apps work fine. T-Mobile did assign a 10 digits telephone number like device number based on ZIPcode entered by me. However, calling the device number got recording saying "At subscriber's request, this phone does not accept incoming call, message CA***58"; where *** means 3 digits number that changed every time when called. Sending text to the device number will get auto-reply stating "Free Msg: Receiver 1NPANXXYYYY unable to receive message - Message Blocking is active. Date: 09/29/2014 6:02 am"; where NPANXXYYYY is the 10 digits device number. Therefore, I am indeed getting mobile version of cutting landline telephone -- only getting Internet access from phone (like dry loop DSL) or cable company. :D

Log into My T-Mobile Online | Access Messages, Minutes & Bills | T-Mobile, it shows I have "Nexus 5 (D820)". In other words, T-Mobile is aware of I am using phone instead of T-Mobile 4G Mobile HotSpot - Orange (which had showed as "MF61 Liberty") or tablet, but still allow it. :)

I tried to port out the DID with $30 pre-paid phone to Ring.to. T-Mobile rejected it due to invalid account number despite per Find your account number | T-Mobile Support, my pre-paid account number should be the phone number. I had to print My T-Mobile Online web pages for $30 pre-paid plan into PDF files then e-mail to Ring.to support to finally have T-Mobile releases the DID to Ring.to today. :(

I am aware of T-Mobile plans to restore Pay in Advance Mobile Internet Monthly Passes for 1 GB from currently $10 back to $20 by the end of this year. If they indeed are doing that which I highly doubt it since it will have higher price than Sprint, my back up plan is to buy FreedomPop Freedom Spot MiFi 500 LTE (it appears this is the only Mi-Fi device they have that supports LTE) for about $162 including sales tax, shipping & handling and always place this Mi-Fi device in my car as I do not go places without my car. My phone will always connect to this Mi-Fi device whenever I do not have Wi-Fi. I consider this back up plan as paying one and half year of mobile data only service in advance for about $10 per month. What do you guys think?

I hope above information provided is useful by others similar situated.

Updated information as of 2014-10-06:

On Tuesday, September 30, 2014 after 7 p.m. I had people telling me in person that I was not answering call. I checked and found out all softphone apps went offline. I used web browser to check web sites, only could reach T-Mobile sites. Eventually, I had to place the SIM back into T-Mobile 4G Mobile HotSpot - Orange and had phone connect to the HotSpot, then Internet connection was restored but with HSPA+ instead of LTE.

Consequently, since Wednesday, October 1, 2014, I have gone back to T-Mobile $30 per month pre-paid plan with 100 minutes talk, unlimited text and data with first 5 GB up to LTE mobile network technology via a new SIM.

Upon additional search, I found out T-Mobile phone and data SIMs are not interchangeable between phone and tablet. :(

As a result, Red Pocket data-only plan is the only option now. :( One can get first ½ GB for just 1¢ that is what I am going to try next. :)